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Old 05-29-2010, 10:42 AM
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Edelbrock 1406 hesitation

My 1406 carb hesitates (a little) if I stab it to the floor below ~3500 rpm. Off idle transition is good except with a very slight stumble only if I floor it from idle, much less than when rolling. Motor pulls clean to 6K, haven't tried taking it higher. I think it is hesitating on the transition to secondarys.

Motor is a 350 chevy in an 83 S10, 487X heads~9.5-10:1 cr, comp xe274, RPM air gap intake, HEI w/msd 8501 kit, spiral core wires, NGK (br6fs) plugs gapped to .040, hedmann shorties w/2.5" duals, 700r4 trans w/stockish converter (2k stall maybe?), 4.10 gears. Timing is 15 initial/35 total (in by 2500) +12 for vac can (full vacuum not ported). Vacuum is 15.5" at 800 rpm.

I've tried different springs, moving the pump arm linkage, jetted from stock to .104's in all corners with a 75-47 rod and 8" spring, upped the squirter from .031 to .033 and yesterday I rebuilt the carb. The hesitation remains.
Currently running .100 w/75-37 rod and 7" spring in the front, .101 in the rear, .033 squirter with the linkage on the inboard hole.

I noticed that the 1405 calls for a .028 squirter stock (thought those were supposed to be dialed richer) and was wondering if it would be worth trying the .024 squirter I got in the kit? (longer duration shot?)

Also wondering if a looser converter would help (it's on my wish list anyways)?

Am I off base that this is a secondary transition problem?

Anything else I have overlooked?

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Last edited by Rhansen; 05-29-2010 at 03:37 PM.
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Old 05-29-2010, 11:26 AM
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hesitation

you overlooked the holley! That's the very reason I switched.

Have you tried ported vacuum to the dist. instead of full time manifold vacuum? Some engines like it that way and some don't. Just like women!
Easy to check buy just capping off the manifold port and move the hose to the port on the front of the carb. Worth a try!
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Old 05-29-2010, 01:29 PM
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Quote:
Originally Posted by sqzbox
you overlooked the holley!
nah, I got a 3310 sitting on the bench
I doubt the vac port is problem but there is a very easy way to be sure, will try it.
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Old 05-29-2010, 01:39 PM
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Has anyone dinked with the secondary tip-in weights? Maybe ground on 'em or filed 'em?
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Old 05-29-2010, 01:50 PM
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Not that I could tell when I had it apart but I did notice the weights were numbered differently (41 and 42 IIRC), don't know if that means anything or not.
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Old 05-29-2010, 03:02 PM
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I have much the same engine configuration in my T-Bucket. 350 SBC, 1406, RPM Air Gap, 487 heads, 9.1 cr, pretty much everything else is stock except for MSD ignition. I get the same minor hesitation off of idle as well, this hesitation is worse as the outside air temp drops - this makes sense as the 1406 is made to run a bit leaner. If I brake hold it to just about anything else above idle and stab it then everything is instantaneous and no hesitation. Any part-throttle stab is smooth. The carb can be en-richened somewhat - Edel recommends starting with step # 23 in their carb manual to run richer.

I called Edelbrock about this a while ago. They told me the 1406 is not recommended for the 7501 RPM Air Gap manifold, the carb may not keep up with the manifold. They indicated that a 1405 would be a better match for the manifold or a Performer Air Gap (among other Edels) would be a better fit for the 1406. Since then I have seen the same advice elsewhere. The RPM Air Gap is made for performance from 1500-6500 RPM while the Performer Air Gap id made for performance in the idle to 5500 RPM range. The RPM Air Gap's performance envelope starting at 1500 RPM may explain the hesitation off of idle.

I went through all the other Edel suggestions just to be sure there wasn't something amiss - accelerator pump adjustment and function, shafts, vacuum leaks, idle mixture. While testing, I found mine has less hesitation on full-time manifold vacuum rather than ported vacuum. Timing is 12 BTDC and all in about 2600 RPM, pulls 21" steady vacuum with a silky smooth low idle.

I was considering changing out to another manifold last time I had the heads off, but put the 7501 back on. This is a street cruiser and the street manners of this engine are just too darn good to start messing with it. It may not be the combo Edel would recommend, but it works very well for me. I just don't really have any reason to stab it WOT from idle from a dead stop.
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Old 05-29-2010, 03:31 PM
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Quote:
Originally Posted by cucumber1949
They told me the 1406 is not recommended for the 7501 RPM Air Gap manifold, the carb may not keep up with the manifold. They indicated that a 1405 would be a better match
I've read this before when searching but no one says why the 1406 is not recommended. Jetting/squirters etc can all be changed, and the throttle bores are the same - so why not the 1406? Fuel passages different or something?

Quote:
If I brake hold it to just about anything else above idle and stab it then everything is instantaneous and no hesitation. Any part-throttle stab is smooth
Mine is sort of the opposite, smoother off idle when floored (maybe cuz the tires go up in smoke?) than it is when anywhere else below 3500 rpm. The only way I can get it to hesitate is by mashing the gas, all other transitions are smooth.


Quote:
I just don't really have any reason to stab it WOT from idle from a dead stop.
The reason I stabbed it from a standstill was to see if/how bad it would stumble (troubleshooting), and because this truck will eventually see some bracket racing. Made sure to find a desolate road to do this since it lays rubber and fishtails for a few seconds on the 1-2 shift and destroys the hides in first. Don't need any extra attention from officer friendly.

Also - just tried switching the canister to the ported source (sqzbox), but it still hesitates, so it is back on full vacuum.
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Old 05-29-2010, 08:18 PM
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[QUOTE=Rhansen]I've read this before when searching but no one says why the 1406 is not recommended. Jetting/squirters etc can all be changed, and the throttle bores are the same - so why not the 1406? Fuel passages different or something?


==================================

The comment the tech made to me was the 1406 would not "keep up" with the manifold. He did not explain and I did not ask him to elaborate at the time. But seeing that the RPM Air Gap is supposed to perform up through 6500 rpm I would think the carb might be somewhat stretched out to feed the engine on the top end and also built to run lean as well. The recommended 1405 is the same cfm rating so it doesn't look like a VE constraint. Sorry I can't shed more light on the issue.
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Old 05-29-2010, 09:03 PM
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After re-reading your initial post, I believe you need a bigger carb. 1406 sounds a little small for your mods. I would think in the area of 650-700 cfm might work better. Also, the shorty headers don't scavenge the exhaust as well as long tubes. Have you experimented with any spacers under the carb?
4 hole or open plenum? Not much room for that under the hood of an S-10 huh?
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Old 05-29-2010, 09:36 PM
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There is a 4 hole wooden spacer under the carb now. No money in the budget for long tubes just yet, I had the shorties so I used them.
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Old 06-07-2010, 06:59 PM
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bump
I e-mailed edelbrock about this last week, still waiting for a reply.
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Old 06-07-2010, 07:37 PM
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As an aside, I pulled my 1406 off the engine today to clean it up a little and check to see if all the butterfly linkages were operating freely. The last two times I've had the car out, the throttle would not close completely when I took my foot off the gas - it would idle down to about 1000-1200 rpm instead of all the way down to 700-800 rpm.

Anyway, I noticed while I had it off that the accelerator pump was not shooting any fuel on the very first advance of the throttle. It would start to shoot after about an 1/8" of throttle travel. Also, when I removed the linkage between the throttle and the pump and moved the pump up and down I feel a momentary but noticable 'catch' or hangup as the pump is returning after depression. My diagnosis is that it needs a new accelerator pump for starters. And seeing that the pump spring seems to provide the last bit of closure on the primary butterflys (through the linkage) that may also be part of the problem.

Anyway, the only reason I mention this in this thread is the reported stumble by the OP (as well as my stumble although slightly different) after stabbing the throttle, which I believe is due to the accelerator pump not delivering enough fuel immediately causing a momentary lean condition until the secondarys kick in and remedy the situation. I'll let you know after I replace the pump.
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Old 06-08-2010, 12:34 AM
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That makes good sense. Sounds like your on to something!
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Old 06-10-2010, 07:50 PM
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Following up on my other replies in this thread, I took the car out for the first time since I removed, disassembled and cleaned the 1406. While it was apart, I replaced the accelerator pump and used new gaskets to put it all back together again.

The high idle problem (the reason I took the unit off the car) has disappeared. Apparently the accelerator pump was hanging up on the last portion of it's return stroke and that was not letting the primary butterfly to close completely most of the time. Also, as a side benefit, the off-idle to WOT stumble has completely disappeared. Hope something here helps the OP.
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Old 06-10-2010, 10:40 PM
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Quote:
Originally Posted by sqzbox
you overlooked the holley! That's the very reason I switched.

Have you tried ported vacuum to the dist. instead of full time manifold vacuum? Some engines like it that way and some don't. Just like women!
Easy to check buy just capping off the manifold port and move the hose to the port on the front of the carb. Worth a try!
word. i used to run eddies, now i run holleys. i will never ever ever go back to an edelbog.
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