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-   -   Misfire, but where? (http://www.hotrodders.com/forum/misfire-but-where-221689.html)

91CamaroDude 07-14-2012 05:16 PM

Misfire, but where?
 
I have a stock 350 carbed motor /w t350. For a while now Iv had a miss after it has warmed up. Timing is probably around 16* and locks out at 35*. Its very odd because, if I retard the timing anywhere passed that I have a bad hesitation if I romp on it until about 4k rpms and then it smooths out. However, if I retard the timing to around 12*, after its warm i wont have a miss at idle. Iv re adjusted the valves, removed the floats from the carb n cleaned 'em out with the jets and secondaries, checked for vacuum leaks, it has new plugs n wires gapped correctly. Im not sure if its in the dizzy or where else to look. :confused:

RWENUTS 07-14-2012 05:42 PM

Vacuum advance hooked up I presume. If so to ported or manifold?
Sounds like too much advance at idle.

91CamaroDude 07-14-2012 05:47 PM

It's manifold. That's what I thought before but if I give it a lower timing at idle* it has a really bad miss or stumble until it reaches a certain rpm that's what cunfuses me the most

RWENUTS 07-14-2012 07:26 PM

Try it on ported and bump your timing up. I ran a sbc at 22* initial with a total of 34* with ported vacuum. Ran super.
An easy test.

91CamaroDude 07-31-2012 03:58 PM

I mentioned before that I had manifold vacuum, however that was a lie. Im not sure why I assumed it was manifold, but after looking around at other forums it is indeed ported. Rookie mistake.

If I increase the Idle RPM to right around 1100 rpms, the miss goes away. It can be first started for the day, or warmed up in this hellacious weather we have all been having, and the miss goes away.

Would there possibly be a leak in the vacuum canister or somewhere internally in the dizzy that is causing my
idle issue? Or once again is that wishful thinking?

The reason why I mention that is because this time last year is when the swap took place. I was limited to the amount of daylight after work plus the heat. No garage accesible, and hood was removed. PLUS my dizzy cap wasnt on until I was really getting ******* done. Why it wasnt on is beyond me. But it was exposed to the elements of heat and some rain. So there had to be some water that got underneath my cap - how long it was in there is unknown.

Thanks for the responses

bigdog7373 07-31-2012 04:24 PM

Try this. Find out what cylinder has the misfire. Move every wire on the dizzy one forward and follow what terminal goes to which cylinder. Then move the plug from the original problem cylinder to a different cylinder than what the terminal is. Then move the wire to a different cylinder also. An example would be if the misfire was on cyl 5, the terminal would change to 7, wire could go to 3 and plug to 8.
Now, once you have done that, run the engine, (remeber to set you timing right), amd find the misfire. If it followed the dizzy, then that's your problem, or if it followed the plug, or wire, etc..

91CamaroDude 07-31-2012 07:12 PM

Well I have replaced plugs and wires and it still has a miss when its warm. But I went out and let it run for a minute or two to see if I could find a dead cylinder with a bottle of water and every single one were sizzling just as much as the other. Now there's a little exhaust leak just after the collectors because I made it out of straight pipe so its not perfect. Would that give me the miss or stumble after its warmed up?

bigdog7373 07-31-2012 07:57 PM

No.
Get a timing light and try it on each wire until you find the inconsistant/ not existant spark.
Once you find it do what I said except without moving plugs and wires. Just the dizzy. If it follows the terminal just replace the whole distributor, not worth messing with imo.

91CamaroDude 08-01-2012 12:15 PM

Okay I clearly had no idea what you were trying to explain in the first response, however I think I understand it a little bit more. I have a timing light, and since I was reading your posts last night I figured what better time to see if I can find a bad wire than at night because I had no idea where to track down the bad cylinder. Tracked it down to cyl #7's wire. (pretty sure just the wire cuz when I was removing the wire from the terminal I didnt think to shut the car off and the terminal shocked the piss out of my finger when removing it haha) I swapped #'s 5 and 7 on the terminal and the plugs, and the inconsistant and lack of spark seemed to follow the wire. Now I have yet to continue with your recomendation because upon figuring out which wire was missing, with the long constant idle it randomly shut off on me. And I could tell that my starter was getting heat soaked because after I turned it off to swap out 5&7 when I went to start it up it at first felt like a weak battery but after it started cranking full rotations it would fire up. It was just the first point of starting.

But Im wondering if I should even go any further in trying to figure out which part of the dizzy or not because this is what has happened before with the little miss iv always had; I would drive it a good distance in this 95+ degree heat, it got to around 210 and had a bad stumble and randomly shut off at a light until I let it cool down. But the temp last night never got above 185..not once. And randomly shut off. There was plenty of fuel in the filter right before the carb, but did not look into the bowl to see if it was boiling.

bigdog7373 08-01-2012 12:50 PM

Yep sounds like a bad wire. Do you have an old set laying around? Just swap the bad one out with one from another set and see what happens. Hopefully it will be gone, but if not then you'll have to check the dizzy. I'll try to explain it better if you end up needing to go that route.

210 isnt overheating for an sbc. What carb do you have? Edelbrocks have been known to cause the fuel to get too hot and spill into the intake. This usually happens when you have a low rise intake and the carb mounted directly to it. Basically it floods the engine out at idle. Can also happen right after shutting it off, makimg it a pain to start.

Another thing to look at is that your advance may be getting stuck, which would cause your hard start you exoerienced. Basically your timimg is too far advanced and is working against the starter.

91CamaroDude 08-01-2012 01:10 PM

Quote:

Originally Posted by bigdog7373 (Post 1579134)
Yep sounds like a bad wire. Do you have an old set laying around? Just swap the bad one out with one from another set and see what happens. Hopefully it will be gone, but if not then you'll have to check the dizzy. I'll try to explain it better if you end up needing to go that route.

Yea ill get a wire here soon and swap it out.

Quote:

Originally Posted by bigdog7373 (Post 1579134)
210 isnt overheating for an sbc. What carb do you have? Edelbrocks have been known to cause the fuel to get too hot and spill into the intake. This usually happens when you have a low rise intake and the carb mounted directly to it. Basically it floods the engine out at idle. Can also happen right after shutting it off, makimg it a pain to start.

I know 210 isnt over heating but it has a steady climb to that point and I will not let it get over that because of fear of premature damage to the motor. Just me

Quote:

Originally Posted by bigdog7373 (Post 1579134)
Another thing to look at is that your advance may be getting stuck, which would cause your hard start you exoerienced. Basically your timimg is too far advanced and is working against the starter

That also does sound like it could be a symptom because when I first assembled and tried to start it, I had my crank and cam gears 180* out and it gave me that Pffff wubba wubba wubba kinda sound like the timing would be working against the starter. Could the advance get stuck after warm up? or would it do it randomly? Only reason why i ask because unless iv been driving it around and its warm it will never do that to me.

bigdog7373 08-01-2012 02:13 PM

The only way the advance could fet stuck is
A. When you rev it, it will get stuck advanced
B. A bad spring. But it would be impossible to time so that's not an option.

Try the new wire and see whst happens.

Also, let the temp climb past 210 if it will. If it doesnt stop by 220 then shut it down because you have a problem.

91CamaroDude 08-01-2012 02:26 PM

Quote:

Originally Posted by bigdog7373 (Post 1579163)
Also, let the temp climb past 210 if it will. If it doesnt stop by 220 then shut it down because you have a problem.


Its funny you actually mention that. When I wired up my elec fans, I always assumed it was going to push the air into the rad to cool it. Turns out I was wrong and now that I swapped the terminals on the fan and it pulls, I havent seen it get above 210. But that is the reason now why if it gets up to that point yes there is really a problem. Will post an update on the wire change and see if the problem is still there. Thanks for your help!

bigdog7373 08-01-2012 02:33 PM

What temp are your fans set to come on at? Also what temperature thermostat do you have?
I like a 180* t stat with the fans set to come on at 195 and off at 185. Yea it's a small margin but keeps it at perfect temperature.

91CamaroDude 08-01-2012 03:57 PM

Quote:

Originally Posted by bigdog7373 (Post 1579170)
What temp are your fans set to come on at? Also what temperature thermostat do you have?
I like a 180* t stat with the fans set to come on at 195 and off at 185. Yea it's a small margin but keeps it at perfect temperature.

I actually have them wired to a toggle switch, with a 160 tstat, and I turn em on a few miles down the road generally around 150 - 160. And with that It keeps it just below 200 on a normal commute to work. If im out toolin around town maybe a little higher but not the 220-230 i used to get before I turned the fan around


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