Plug Heat Crossover on Manifold Cause Hesitation?

palerider94 · May 17, 2006

I just installed new intake gaskets on my manifold. Upon advice from a local gear head I used the plugs that came with gasket that plug ports going under carb on manifold. I think are called the heat cross over on the manifold. Was told it would run cooler with this done. Although it may impact choke operation in cold weather - since it will be a fair weather car was not too concerned.

I do now have some hesitation on take off that I did not have before. Thought it may be timing was too advanced so I reset and I still have hesitation - had to adjust idle/fuel mixture to get rid of some - but still have it. Just wondering if I can rule th cross over on the manifold as a source of the problem. Hoping I can - don't want to pull manifold off again. I'll probably pull carb and check bowls just to ensure they did not get bounced around during the install. Appreciate any feedback. thanks

302 coupe · May 17, 2006

it won't cause any hesitation, as a direct result of plugging it at least. However, at least on my car, doing that kept the intake cooler on start up causing a slight stumble, kinda like a choke related issue would do. Once the intake warms up, it goes away. My engine has a pretty big cam and the choke horn has been milled off the carb, so its kinda picky about stuff like that. As to whether or not blocking the exhaust crossover adds any power.....tough to say. It should, in theory, keep the intake cooler, but the heat still conducts through the heads and by the hot underhood air, so its not cool by any means. At least it doesn't have 1300* exhaust running through it anymore.
I'd say to let the engine get throughly warm, like after 15 minutes of driving, and see if it still stumbles. At this point the intake should be warm enough where the lack of exhaust crossover should have no effect. If you still have a stumble, start looking elsewhere. If the stumble goes away when the engine is warm, you might consider removing the plugs to allow the exhaust crossover to work again.

palerider94 · May 17, 2006

No still there when warm - will continue to look other places. Appreciate response. I'll start doubling checking evrything. thanks

D.Hearne · May 17, 2006

Check the accellerator pump, to see if it's operating properly. If it's a Holley, you may need to adjust the slack out of the linkage, add a larger 50cc pump, or play with the pump cam or squirters.

palerider94 · May 17, 2006

That will be the next thing I check. Since it started after I changed intake gaskets - thought it was something related to what I did. I will check accelerator and floats next but since they were okay before gasket change I'm not real hopeful this is it. But checked vaccums, timing and it does not seem to be the probem - running out of things to check. Thanks

jbuening · May 18, 2006

Check engine with a vacuum gauge. It's possible the intake gaskets didn't get a good seal and you have a vacuum leak.

Max Power · May 18, 2006

The heat crossover is to help heat up the intake charge much sooner. Many cars had truoble with fuel seperating from air on cold engines, and running a heat crossover helped keep the fuel atomized sooner on a cold engine.

I have blocked the crossover on many engines and had no problems. Too much heat on a fully warmed engine robs horsepower.

palerider94 · May 18, 2006

I've used vaccum gauges to check for carb setting - but how will it tell you if you have a vaccum leak?

jbuening · May 18, 2006

for one, your readings will be lower than normal. May also have an erratic needle. There are numerous websites that have guides and even animated gauge readings.

http://www.iwemalpg.com/Vacuum_gauge.htm
http://www.earlycuda.org/tech/vacuum2.htm
http://www.classictruckshop.com/clubs/earlyburbs/projects/vac/uum.htm
http://www.centuryperformance.com/vacuum.asp

D.Hearne · May 18, 2006

You can check for leaks topside with a spray can of carb cleaner. Bottom side of the gaskets? Maybe introduce some gas fumes into the PCV inlet. Or maybe not, I'm not sure if that would work, given the PCV sucking them up after they've circulated thru the motor.

palerider94 · May 18, 2006

Took a propane torch and turned gas on and check around all areas - no change in engine idle.

Here is what I have done:
Checked for vaccum leaks
Just pulled carb bowls thought it may have got bounced aroubnd - they were okay.
Set timing at +5 over stock had at 10 and it was causing starter overheating - although no pinging.
check plug wires all in right order

Everything weas running fine prior to intake gasket changes. I think my next step is change the accelerator pump squirter - then maybe vaccum advance. If all else fails I think I need to find someone locally who can tune figure out what is going.

palerider94 · May 19, 2006

One thing I forgot to mention was that when I was reading vaccum links above stated you should use a simple "manifold" vacuum source. "This must not be "ported" vacuum that rises as RPM increases, such as vacuum from the distributer that drops when idling".

I hooked to valve on maifold that has a number of vaccum ports out of it that various area plugged into and vaccum increased as I gave it gas. Is that right? If so where do I find non ported vaccum area?

jbuening · May 19, 2006

Yes you did it correctly. The ported source is located on the carb. What kind of readings were you getting with the vacuum gauge hooked up to the manifold? Were the readings steady or did the needle bounce around alot? What is your idle set at?

palerider94 · May 19, 2006

It was steady at 16 - did not bounce around - when I gave it gas it increased. Don't have a tach so not sure of RPMs - need to get a tach I can connect up for tuneups.

D.Hearne · May 20, 2006

palerider94 said:
Took a propane torch and turned gas on and check around all areas - no change in engine idle.

Here is what I have done:
Checked for vaccum leaks
Just pulled carb bowls thought it may have got bounced aroubnd - they were okay.
Set timing at +5 over stock had at 10 and it was causing starter overheating - although no pinging.
check plug wires all in right order

Everything weas running fine prior to intake gasket changes. I think my next step is change the accelerator pump squirter - then maybe vaccum advance. If all else fails I think I need to find someone locally who can tune figure out what is going.

Did you set the timing at 10 degrees BTDC ( Before Top Dead Center) or ATDC ( After Top Dead Center) ? If it was hard for the starter to turn the engine over, sounds to me like the timing's still retarded , which would be where 10 degrees ATDC would be. Advancing will put it at the BTDC side of "Zero" degrees on the balancer. Your balancer may have also slipped too. If it did and slipped too far, that will also throw it out of balance as well.

palerider94 · May 20, 2006

To be honest not an expert on timing. Basically, set 5 degrees above stock setting at idle with distinb vacuum plugged. Was at 10 degrees above stock setting at idle and it was putting a strain on the starter. Not sure about how to set BTDC or ATDC.

D.Hearne · May 20, 2006

Look at the balancer marks. There you will find this: ATDC 10 l l l l 0 l l l l 10 l l l l 20 l l l l 30 BTDC You want to set the timing at about 10-12 degrees on the BTDC side. Setting it on the ATDC side is retarded, the spark's going off after the piston starts back down the bore, the full flame doesn't happen then untill it's reached the bottom and started back up on the exhaust stroke. The flame needs time to reach it's fullest point to exert the maximum push on the piston, so it needs to be ignited before the piston reaches top dead center. The more rpms the engine's turning,the faster the piston's moving and thus the spark needs more lead time the to get the flame at it's optimum point for maximum push.

palerider94 · May 20, 2006

Thanks- I'll double check - I think it have it at 6 on BTDC plus advanced another 5. So should be where you suggest.

Only 3 things I did different when changing gaskets.
1) Pertonix - full 12 volts different igntion wire
2) Plug exhaust intakes on manifold came with gasket (told it would run cooler)
3) Reset timing

Hesitation seems to be from being lean - do you think that pertronix with full 12 could cause this - may need more gas from squirter when stepping on it - was going to change accelerator squiter to see if any difference - what do you think? Assuming I have timing right.

D.Hearne · May 20, 2006

If anything adding a Pertronix unit lessens the engine's need for fuel (easier starting) not the other way around. What intake do you have anyway ?

palerider94 · May 21, 2006

Have perfomer 289 intake.

Plug Heat Crossover on Manifold Cause Hesitation?

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