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Old 04-16-2012, 09:13 PM
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Engine RPM is Intermittent

Hi guys I am experiencing some rpm changes almost to where the engine wants to die but it doesnt. The wierd thing is it doesnt do it all the time. Some times it will do it when I first time i start it up after sitting and somtimes it wont. I could fire it up and it will be fine and all of a sudden after driving it for a half hour it will start up. I dont understand I checked for a vacume leak when it is running smooth and it shows no symptoms in that case. Whatever the casuse may be it seems very intermittent. Maybe if anybody has any suggestions that could help me out i would appreciate it.

I am running a pertronix billet distributor, second strike coil for my ignition system. if there is any other information that you might need let me know.

Thank you Joseph

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Old 04-17-2012, 12:40 AM
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Quote:
Originally Posted by 406MOUSE
Hi guys I am experiencing some rpm changes almost to where the engine wants to die but it doesnt. The wierd thing is it doesnt do it all the time. Some times it will do it when I first time i start it up after sitting and somtimes it wont. I could fire it up and it will be fine and all of a sudden after driving it for a half hour it will start up. I dont understand I checked for a vacume leak when it is running smooth and it shows no symptoms in that case. Whatever the casuse may be it seems very intermittent. Maybe if anybody has any suggestions that could help me out i would appreciate it.

I am running a pertronix billet distributor, second strike coil for my ignition system. if there is any other information that you might need let me know.

Thank you Joseph
fuel injection ,carb? manual fuel pump, electric pump. are you running the ignition box also with the dist.
a lil more info, sounds like a fuel problem to me but i havent heard it run so its hard to say.
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Old 04-17-2012, 02:01 AM
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Quote:
Originally Posted by inkfreak1976
fuel injection ,carb? manual fuel pump, electric pump. are you running the ignition box also with the dist.
a lil more info, sounds like a fuel problem to me but i havent heard it run so its hard to say.
It is a carb 750 mechanical demon (not pleased with but gets the job done for now) I am running a 6 psi electric pump at the rear and a mechanical with 1/2 inch line to 3/8 to carb. not running a ignition box jus a rev limiter. i figure it could be fuel or ignition but dont know which one. the car does not backfire or miss or anything like that. i do have a fuel pressure gauge on car and its reading from 8 to almost 9 psi at idle. im not sure if that could be the problem why its doin this? if that could be to much psi whats a good fuel pressure regulator to use? could week advance springs cause this ive had the dist for 7 years in my old motor and havent replaced springs could this be a cause? or bad coil?

Thanks for your reply
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Old 04-18-2012, 02:15 AM
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Quote:
Originally Posted by 406MOUSE
It is a carb 750 mechanical demon (not pleased with but gets the job done for now) I am running a 6 psi electric pump at the rear and a mechanical with 1/2 inch line to 3/8 to carb. not running a ignition box jus a rev limiter. i figure it could be fuel or ignition but dont know which one. the car does not backfire or miss or anything like that. i do have a fuel pressure gauge on car and its reading from 8 to almost 9 psi at idle. im not sure if that could be the problem why its doin this? if that could be to much psi whats a good fuel pressure regulator to use? could week advance springs cause this ive had the dist for 7 years in my old motor and havent replaced springs could this be a cause? or bad coil?

Thanks for your reply
the normal running psi for a holley carb is about 8 psi at the carb, wich doesnt make since because you say that your running a 6 psi pump and at idle it reads 8=9 psi, where is your pump located at in or near the tank or at the fire wall.
and why run 2 differant hose sizes. 3# do you have a gauge at the carb whats that say.
to me it sounds like you have a fuel supply problem, i would first change your pump to something that puts out at least double the amount of the needs of the carb, change the fuel lines to one size maybe 3/8, and run from the fuel pump to a regulator after the regulator to a guage, adjust the regulator to abot 8 psi to the carb always have a gauge at the carb also so that tells you alot of trouble shooting in just a couple of quick glances. if your haveing fuel problems you can adjust your psi at the regulator up or down to get that correct. from there check your float bowls make sure thats correct.
to me it sounds like your pump is working to hard and my be burning up
weather or not you need to change your ignition or not at least your fuel situation will be correct. and very easly diagnosed and will have the fuel when you need it incase you get a sudden case of lead foot like me.
let me know how it turns out. or need help with any part of my advise. good luck
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Old 04-18-2012, 02:20 AM
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after re reading your post just to keep her running, check your floats first it may be just a simple float adjustment. but i would deff. change the set up because youll rob the carb of fuel with the current set up during high rpm situations ie; race drag or passing. i would bet the floats would be the cause right now. and what is the engine your running and some specs you might just be over jetted. let me know i think that im onto it just need some info
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Old 04-18-2012, 08:19 PM
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RPM starts to drop.

Quote:
Originally Posted by inkfreak1976
after re reading your post just to keep her running, check your floats first it may be just a simple float adjustment. but i would deff. change the set up because youll rob the carb of fuel with the current set up during high rpm situations ie; race drag or passing. i would bet the floats would be the cause right now. and what is the engine your running and some specs you might just be over jetted. let me know i think that im onto it just need some info
this is the setup i am running which is half inch line from the tank with a inline 6 psi mallory electric pump close as possible to rear of tank continues with 1/2 inch line all the way to the mechanical holley high volume pump. All the eledtric fuel pump is to ensure that i am getting a constant fuel to the mechanical pump. I do have a fuel pressure guage and it reads at idle (this is when it is idling at 1000 rpm or so 8 1/2 to 9 psi) i have not checked to see what the fuel pressure is when the car starts to drop in rpm becuase i am fethering the throttle to keep it running and by doin that for awhil it will like clear up and idle fine again.

Let me know what you think and we can talk about maybe some type of process of elimnation. I apreciate your help and advice. below are some engine specs of my motor.

Thank you



engine specs

engine is a 410 smc

Bore: 30 over
Stroke: It is a 6 inch rod

this is the piston specification that i got with the motor they are Racetec pistons. i do have a picture of what the piston looks like if you would like me to email you a pic or somthing.

The actual piston compression is 11 to 1

Engine Information
Head type: 40/60 SHIFT
Bore diameter: 4.165 in
Stroke: 3.750 in
Rod length: 6.00 in
Displacement/cubic: 408.7
Comp distance 1.125 in
Ring Info
Ring Number: AT8165 (not sure if this helps)
Rail info
Rail number: 3.845-168
Wrist Pin Info
Pin Type: chamfered
Pin number: 927-2700-51-15c
Diameter: 0.927 in
Length: 2.700 in
Piston Information
Piston type: dome diameter
Diameter 4.1620 in
Weight: 456 grams
Deck to crown thickness: 0.220
Forging type: A4123F N/C
Dome Volume: -.400 cc
Gauge point: 0.200 in
Ring groove width
Top Ring: 0.0640 in
2nd ring: 0.0640 in
Oil ring: 02180 in
Land width
Intake- depth: 0.280 in ,angle: 23.0 degrees
Exhaust- depth: 0.280 in ,angle: 23.0 degrees

im not sure wat piston deck height is but i do not piston was flush with the deck if that helps.


gasket thickness im using mls 1144 fel pro
-gasket bore: 4.200"
-comp volume: 8.9cc
-thickness: .040"

i have AFR 210 heads with 75 cc chambers

the drive train is a complete roller
The camshaft is a solid roller specs are:
lift: .630
Lobe Centers: 106
intake opens at 21 degrees close at 52 degree
exhaust opens at 54 degree close at 22 degree

intake is 253 @ .050
0.0200 is 284

exhaust is 256 @.050
0.0200 is 288
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Old 04-18-2012, 09:55 PM
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ok i jus got home and its on the verge of getting dark and i started up the car and wanted to check the fuel pressure and double chek inches of vacum in drive and noticed that my headers were glowing again i thought i had fixed this problem but appernty not is this too much fuel or not enough? I am running a 3.5 power valve and i believe the inches of vacum bounces between 7 and 8 inches in drive, jets in primary are 78 and 84 in secondary. i dont think the power valve is blown the car has never backfired and the carb has the check ball if it did. maybe this can help you out as well my wheels are spinning on this one. oh and my timing is set at around 32 total with and initial is 17. car fires right up and does not run hot so i think timing is good but what do i know.

Last edited by 406MOUSE; 04-18-2012 at 10:03 PM.
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Old 04-18-2012, 10:30 PM
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Quote:
Originally Posted by 406MOUSE
this is the setup i am running which is half inch line from the tank with a inline 6 psi mallory electric pump close as possible to rear of tank continues with 1/2 inch line all the way to the mechanical holley high volume pump. All the eledtric fuel pump is to ensure that i am getting a constant fuel to the mechanical pump. I do have a fuel pressure guage and it reads at idle (this is when it is idling at 1000 rpm or so 8 1/2 to 9 psi) i have not checked to see what the fuel pressure is when the car starts to drop in rpm becuase i am fethering the throttle to keep it running and by doin that for awhil it will like clear up and idle fine again.

Let me know what you think and we can talk about maybe some type of process of elimnation. I apreciate your help and advice. below are some engine specs of my motor.

Thank you



engine specs

engine is a 410 smc

Bore: 30 over
Stroke: It is a 6 inch rod

this is the piston specification that i got with the motor they are Racetec pistons. i do have a picture of what the piston looks like if you would like me to email you a pic or somthing.

The actual piston compression is 11 to 1

Engine Information
Head type: 40/60 SHIFT
Bore diameter: 4.165 in
Stroke: 3.750 in
Rod length: 6.00 in
Displacement/cubic: 408.7
Comp distance 1.125 in
Ring Info
Ring Number: AT8165 (not sure if this helps)
Rail info
Rail number: 3.845-168
Wrist Pin Info
Pin Type: chamfered
Pin number: 927-2700-51-15c
Diameter: 0.927 in
Length: 2.700 in
Piston Information
Piston type: dome diameter
Diameter 4.1620 in
Weight: 456 grams
Deck to crown thickness: 0.220
Forging type: A4123F N/C
Dome Volume: -.400 cc
Gauge point: 0.200 in
Ring groove width
Top Ring: 0.0640 in
2nd ring: 0.0640 in
Oil ring: 02180 in
Land width
Intake- depth: 0.280 in ,angle: 23.0 degrees
Exhaust- depth: 0.280 in ,angle: 23.0 degrees

im not sure wat piston deck height is but i do not piston was flush with the deck if that helps.


gasket thickness im using mls 1144 fel pro
-gasket bore: 4.200"
-comp volume: 8.9cc
-thickness: .040"

i have AFR 210 heads with 75 cc chambers

the drive train is a complete roller
The camshaft is a solid roller specs are:
lift: .630
Lobe Centers: 106
intake opens at 21 degrees close at 52 degree
exhaust opens at 54 degree close at 22 degree

intake is 253 @ .050
0.0200 is 284

exhaust is 256 @.050
0.0200 is 288
i think you gave me what i was looking for,
you could try this because im not sure what kind of fuel line your running im not sure how hard this will be to do. i would run the fuel line straight from the electric pump to the regulator. check your floats and adjust air/idol if needed see how that runs. my thinking is that your some how over filling the the float bowls and instead of it trickling into the metering blocks its forcing the fuel into the metering blocks which is the same as flooding the engine, thats why you have to feather the throttle to keep it running, your giving it more air. now this is not a full fix this is just to see if im right, i think that the electric pump is cavitation the diaphragm of the mechanical pump.
so when your at a idol, the electric pump is trying to push past the diaphragm, when your driving or getting into it the mechanical pump is trying to pump that's why you have the extra psi, but with the rpm of the engine increasing the pump is also increasing the fuel delivery. and i would bet also theres air bubbles in the line also from the cavitation. which isnt good.
the dom. carb isnt a bad carb they just flow alot of fuel, and might have to jet down but i would try this out see how it runs. if it runs better with out the problem then change your electric fuel pump to dump 2xs the amount needed to the regulator. good luck let me know how it turns out
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Old 04-18-2012, 10:47 PM
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Quote:
Originally Posted by inkfreak1976
i think you gave me what i was looking for,
you could try this because im not sure what kind of fuel line your running im not sure how hard this will be to do. i would run the fuel line straight from the electric pump to the regulator. check your floats and adjust air/idol if needed see how that runs. my thinking is that your some how over filling the the float bowls and instead of it trickling into the metering blocks its forcing the fuel into the metering blocks which is the same as flooding the engine, thats why you have to feather the throttle to keep it running, your giving it more air. now this is not a full fix this is just to see if im right, i think that the electric pump is cavitation the diaphragm of the mechanical pump.
so when your at a idol, the electric pump is trying to push past the diaphragm, when your driving or getting into it the mechanical pump is trying to pump that's why you have the extra psi, but with the rpm of the engine increasing the pump is also increasing the fuel delivery. and i would bet also theres air bubbles in the line also from the cavitation. which isnt good.
the dom. carb isnt a bad carb they just flow alot of fuel, and might have to jet down but i would try this out see how it runs. if it runs better with out the problem then change your electric fuel pump to dump 2xs the amount needed to the regulator. good luck let me know how it turns out
What about the glowing of headers at idle? also what if i turn off or disconect the electric pump to see what it does with just the mechanical?
I do not have a fuel regulator on the motor.
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Old 04-18-2012, 11:25 PM
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Quote:
Originally Posted by 406MOUSE
What about the glowing of headers at idle? also what if i turn off or disconect the electric pump to see what it does with just the mechanical?
I do not have a fuel regulator on the motor.

i also forgot to mention that when i screw in the idle mixtures on the carb it raises the engines RPM instead of killin the motor so i have the 4 idle mixure screws set at 1 1/2 turns out. im not sure why this is doing this i have changed metering gaskets and all that. i have never messed with the air bleeds all that stuff is stock settings
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Old 04-19-2012, 01:34 AM
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Quote:
Originally Posted by 406MOUSE
What about the glowing of headers at idle? also what if i turn off or disconect the electric pump to see what it does with just the mechanical?
I do not have a fuel regulator on the motor.
i would think that maybe, detanation or that you cam duration is bleeding off to fast, basicly leting the exhaust valve open during the ignition of the fuel in side the cyl. for the fuel problem question i dont think that youll be able to pull fuel from the tank if you just kill the power to the electric pump and let the mechnical pump go at it, if its a easyer swap you can try eather one thats a easyer swap. but i urge you to get a regulator with a guage i think summit sells a set for under 50 bucks. weather you use the mec. pump or the elec. pump a regulator is very key to makeing sure your not over supplying your float bowls. hell for a qwick test start the car see where the fuel leval is eather threw the site glass or removeing the bowl screw in the site glass i like to set mine at about a 1/4 to 1/2 of the site glass, the screw type should just barly trickle out. take a reading at first start up. then wait for it to start with the problems, if you need to wedge the throttle open a bit to like 1200 rpm if needed to keep her going do the same testing, if the results are differnt then a regulator would be helpfull to keep the bowls correct. you and also adjust the needle valve if needed for the floats, but i would get a regulator first set it first to like 7 psi check your sit holes if its not right increase you fuel psi to 8 check again if not right go to 9psi, if at 9psi in wich you dom should be running at youll have to adjust your float.
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Old 04-19-2012, 01:54 AM
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as for the glowing headers im kinda thinking to much advanced timeing, when you set the timming did you set with a degree wheel for any advace timing or did you go with stock timeing marks,
when you advance the timming yes you get better response but you can also change the valve timing enough. and at 11;1 comp. it should be bleeding off just a bit of the compression before it ignites. but if you have to much advanced timing the e valve will open to much before ignition leting pure flames come right out the exhaust. and with a 106 duration thats tight for that engine that your running i would almost go 108 to 112, bet it purrs nice though at that duration, not much lope. i wish you could just runn it by my house and i could probly figure it out for you but im in lovespark il im unsure where your at. and if its something i cant figure out i know almost to many people that could figure it out. but start out with the fuel problem first. for as much as you have into this engine getting a regulator is a must bro. what kinda headers are you running they might just be to small for your application just a thought. if you know the size of the pipe that might be helpfull also. let me know
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Old 04-19-2012, 02:01 AM
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Quote:
Originally Posted by inkfreak1976
as for the glowing headers im kinda thinking to much advanced timeing, when you set the timming did you set with a degree wheel for any advace timing or did you go with stock timeing marks,
when you advance the timming yes you get better response but you can also change the valve timing enough. and at 11;1 comp. it should be bleeding off just a bit of the compression before it ignites. but if you have to much advanced timing the e valve will open to much before ignition leting pure flames come right out the exhaust. and with a 106 duration thats tight for that engine that your running i would almost go 108 to 112, bet it purrs nice though at that duration, not much lope. i wish you could just runn it by my house and i could probly figure it out for you but im in lovespark il im unsure where your at. and if its something i cant figure out i know almost to many people that could figure it out. but start out with the fuel problem first. for as much as you have into this engine getting a regulator is a must bro. what kinda headers are you running they might just be to small for your application just a thought. if you know the size of the pipe that might be helpfull also. let me know
yea i hear ya i will be getting a regulator tomorrow. the cam has been deggred in do you think maybe i should take timing down a couple degrees to like 30 total and see what happens. im running patriot exhaust long tube headers they are 1 in 5/8. yeah i am pretty far from ya i am in temple city CA.
Whats the best way to check to see if power valve is to big as if its still staying open at idle or to check if its blown?
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Old 04-19-2012, 02:25 AM
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http://www.carcraft.com/techarticles...e/viewall.html
check this out good info in this article.
http://www.holley.com/data/Products/...199R9786-2.pdf
this one is technicly awsome info, and they have a tech line you can call also.
give them a try. but take care of that fuel pump thing first before resetting anything, and a regulator with a guage.
something like this it doesnt have to be this one, but this has everything you need.
http://www.summitracing.com/parts/AEI-13205/
http://www.summitracing.com/parts/AEI-15632/
those are regulators
for fuel pumps something like this will be just fine
this one will rock your nuts off
http://www.summitracing.com/parts/HLY-12-815-1/
but you can get away with this
http://www.summitracing.com/parts/SUM-G3136-2/
take a look at this stuff and let me know
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Old 04-19-2012, 02:41 AM
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Quote:
Originally Posted by inkfreak1976
http://www.carcraft.com/techarticles...e/viewall.html
check this out good info in this article.
http://www.holley.com/data/Products/...199R9786-2.pdf
this one is technicly awsome info, and they have a tech line you can call also.
give them a try. but take care of that fuel pump thing first before resetting anything, and a regulator with a guage.
something like this it doesnt have to be this one, but this has everything you need.
http://www.summitracing.com/parts/AEI-13205/
http://www.summitracing.com/parts/AEI-15632/
those are regulators
for fuel pumps something like this will be just fine
this one will rock your nuts off
http://www.summitracing.com/parts/HLY-12-815-1/
but you can get away with this
http://www.summitracing.com/parts/SUM-G3136-2/
take a look at this stuff and let me know
hey thanks for the info ill take a look at that i will be getting regulator tomorrow. I forgot to mention when i take the plug off the carb to check the engine vacum i get some fuel that comes out of it and the gas is just below the site glass where you can barely see it. whats that sound like it could be?
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