Baffled
 

I ran my car at Sonoma and everything was fine. Did a rear gear swap but didn't drive the car till I installed new brake pads.

Problem......car is hesitating under load. I can goose the throttle with car in neutral with no issues but when I drive it and open the secondary's up the car is hesitating under load with slight pops out the exhaust.
So far I have torn the carburetor apart twice, replaced power valve and accelerator pump diaphragm, checked float level, checked and tightened my fuel lines, replaced plug wires, replaced dizzy cap(had a crack in it), and checked a few of the plugs to see if they were fouled.

Not sure if its a lean miss or electronic.

Any other suggestions?

Is your fuel pump putting out enough gph?

It has in the past and has been on the car for 4 years now with no changes to engine. It could be on its way out though.....

Odd thing is that car was running fine at the track a few weeks ago. It sat in the trailer for a few hot days afterwards and then I took it to get a gear swap. Just seems odd that it would do this after running fine at the track.

Just did a coil swap so I can rule that out.

Pull all your plugs and report color or condition.

1,3,5, & 7 look the same. dry and medium charcoal colored. taking five....its gotta be over 100 in my garage

After checking plugs, check distributor, then check plug wires and measure resistance/ohms with meter. Wires should measure very low resistance. Under load a wire that has high resistance will cause similar issue.

You mentioned a gear swap, what did you go from, and to?

Thanks Jay.......looked for my multimeter this morning and couldn't find it. I used it in the house last so it has to be around here somewhere. Wire are new though.

Plugs 2,4,6, & 8 look the same as 1,3,5, & 7.

Went from 3.42's to 3.73's

Checks them wires for cracking and arch marking....how was that bronze gear?

Plug wires are new. I'll pull distributor and check the gear next.

Gae when you say hesitating under load, is it a stumble/miss and then builds rpms?

Its an intermittent hesitation that doesn't stop until I let off.

Stand by for some pics.

OK, so here is a pic of the cracked cap that I replaced that I thought would fix the issue.

http://i851.photobucket.com/albums/a...torpics044.jpg

Hers a pic of the rotor I just pulled off. Notice the broken portion to the upper left of the screw. That's a weird deal there

http://i851.photobucket.com/albums/a...torpics045.jpg

So it misses from the time you matt it until you hit redline? Or is it only initially and cleans up?

Where is the timing?
Have you checked the fuel pressure at WOT?

The gear change may require you to install a slightly bigger accel pump cam on the secondary side. Meaning, more volume initially. I say this because you should be accelerating a bit quicker which means you are gaining rpm faster.

That cap looks short, are you sure it's the right one?

This is a guessing game without more info, but presume fuel is getting to the carb, your wires/spark is good and timing events from the distributor are as they should be. Do you have PTFE fuel hose forward of the pump? Slight cracks (even on the return side) will do that. Also pull the valve covers and inspect just in case.

I've also seen internal detonation cause this issue (hope not!), but if you don't find the issue do a quick compression check. Fingers crossed it's something simple Bro :thumbsup:

Yes...as soon as I hit the secondary's until I let off.....and that is exactly what I was thinking Todd......more fuel may be needed.

Havent checked fuel pressure or timing yet.

Stand by....more pics

Pic of rusty reluctor
http://i851.photobucket.com/albums/a...torpics047.jpg

Plugs all being consistent rules out compression and likely any other mechanical cylinder issue. The valve springs probably need checked but I doubt it's the problem here as it would likely be a high rpm misfire.

A worn distributor gear will retard the timing and cause a pope and misfire. Ask me how I know...

Check the fuel pressure and timing before you waste more time.

And now the million dollar question. Above is a spare MSD distributor. Below it is the one I pulled out of the car with the bronze gear (which is still in good shape.)
Can you guys tell me why one gear is higher than the other because I don't have a clue.

http://i851.photobucket.com/albums/a...torpics046.jpg

Different application or the gear is on upside down.

Upper distributo has Gear on upside down. Push roll pin out and flip it. Sound like a fuel pressure issue, not keeping up with demand or fuel quality?

LOL....reminds me of a conversation I heard at a homes for humanity site "the head of the nail is on the wrong end".... "ahh Its upside down"

That pic brings back bad memories... I put the new gear on my distributor backwards like that when getting ready to put my engine in my car. Took me about a week to figure out why the distributor wouldn't fully seat.

Was looking back through pictures i took as I pulled everything apart, saw a picture of the distributer before the gear change a BINGO...a light goes off in my head.

You want to know whats even funnier.....it came from MSD that way :lol:

So the next million dollar question..........50cc accelerator pump or bigger jets.

I got a SWAG that won't waste any more of your money.

Pull your filter off and blow through it. If your ears pop, its 30% plugged. If an eye pops out then its 50%. If you crap your pants its just Miller 30. LOL

Hey, so news flash......was talking to Joe Pecavar about springs and bushings for the new dizzy and he says go with what you had because that's how we tuned it. He asks me what bushing the old dizzy had in it. I go to look and the mushroom cap that the weight rides on was gone. Guess what cracked my distributor cap and rotor and has been screwing up my timing? :lmao:

Well, I was going to post up and say its an ignition issue, not a carb issue. But looks like you may have found the culprit!!

Yup....Definitely an ignition issue. Come to think of it.........if your plugs are a medium charcoal color that right there tells you your getting motr than enough fuel :sieg:

Not unless you shut it down at wot. You are looking at the idle burn.

Your total timing should still be fine without the bushing. That effects how much initial timing you have. Now, I can see the bushing bouncing around in there causing the misfire.

No --- As Todd stated -- that only works at drag racing where you're able to shut down after a WOT run....


There are also ways to read timing on the spark plug "strap"... by where it changes color. The color change needs to be a line right across the apex of where the strap makes the turn. But now we're getting really old skool in the pit dyno.


Hope the distributor is the issue -- certainly points to an issue.

What color bushing you running? I would think BLACK.... which would be the 18* stop bushing... and with good heads and good fuel your total timing should be maybe 34 to 36* all in at 2500 to 3000 rpms??

Going with the blue bushing which is basically the one that comes with the distributor and then running the blue springs. I think full advance kicks in at 2900? Have to recheck but wanted to say thanks for the help buddy.
There is a mushroom top with a stud that the weights slide over and the cap completely wore down, broke off, and them was flying around in the distributor. So glad I found out what cracked the distributor cap crack.

The STOP BUSHING is under the plate that the weights attach to... you can't see it from the top at all...

Just saying.

The two light blue springs should work well. There's a graph in the MSD installation manual that shows you all the combinations of springs and were they come in.

Blue stop bushing gives you 21* of advance total FROM the initial.... so to get 36* total - your initial has to be set at 15*


As usual -- I write this stuff so OTHER GUYS that are reading these threads -- and don't know -- can read 'em and see what we're talking about.

Got it. Thanks Greg. You cant see the bushing because its recessed in the plate and covered by the lock nut that secures it in place but I figured out which bushing was in the distributor by looking at the one that wasn't in the kit. Wasn't sure what to set initial timing at but shooting for 32.5* total so looks like I'll be looking for 11.5* initial.

I found that my engine needed all the initial advance I could get. It cleans up the plugs at idle, better cold idle performance, and improved low speed drivability. I know you have a mechanical cam. I'd run the biggest bushing. I actually had a custom bushing in mine that would render 24 degrees initial with 34 total.

Best power was at 32.5* on the dyno? Didn't think your 23* heads were that efficient...

Going with the blue bushing because that's what we dyno tuned the engine with. You cant really tell if your running the right jet sizes in your carb when dyno tuning because you don't have the air cleaner on and the temps are a lot cooler which means the carb is getting fed cooler, cleaner air. With air cleaner on and in 90* plus weather at the track air intake and quality changes. The plugs have had the same light charcoal look from the last time I looked at them which means I am getting a bit to much fuel but didn't bother changing jet sizes in the carb because I want to play it safe and splash a bit more fuel in there but this next time around I'm going to drop a couple jet sizes and see how the car feels. I'm running 84's in the secondary side now but cant remember what I'm running on the primary side.

Yup. Good point though.

Yeah that motor isn't going to like 10 degrees initial... and the rule is always -- the most initial advance you can get without having the starter motor struggle too much or you get engine kickback...

Stock baby cam no compression motors in Buicks idle at 10*'s....


If you ran the black bushing --- that's 18*'s... so you'd end up with 16* initial and that motor can handle 16* initial easy....

You're probably idling around 900+ RPMS is my guess...

I think the Mustang is up around 1200+ and then it barely idles... Sounds like a thrashing machine.

In the old drag race days we'd run a lockout and just dial in the total timing and lock the distributor... then we'd add a coil cut off switch so we could spin the motor around without any spark until she was spinning good - then hit the switch and WHAM! She's fire off good! LOL ---- You need one of those set ups!!

Thems some pretty good heads! :thumbsup:

I think Rob's old dinosaur heads made best power at like 48* :lol: