Pinto bucking / no power in the corners

[redcar9]

Finally got out for more than just 8 minutes. Still chasing problems.

The car will have no power when any steering input is applied. The keyhole (turn 5) shows this, braking, downhill and a right hand turn. I'm full throttle on the car and there is no acceleration until a few seconds on the back straight. The car also has no power in 3rd gear, I top out at 107-111mph back straight of mid-ohio. I have been told I should be able to hit 130mph.

1. Carb was looked at by Ivey, they suggested increase the level of the in the bowl, this helped a little.
2. spark gap was about 0.036" (next time I'm putting it at 0.026")
3. The valve lash on both intake/exhaust was ~0.016" measured cold. (going to change to the recommended 0.008 and 0.01")
4. Cold compression with throttle open and all 4 plugs removed.

• #1 178psi
• #2 147psi
• #3 155psi
• #4 155psi

Aim data
https://www.dropbox.com/scl/fi/0u0sd...=rkhdpoj2&dl=0


https://youtu.be/13VgajdP_UM?si=2WcyWB9qmJTzG12t

[2BWise]

Have you checked the timing?

[Purple Frog]

What 2B said. Timing.
Plus what gear set is in the car? What rpm at 110?
With the pinto in race mode you should never get below 5500 rpm.
If you are trying to drive out of T5 at 4500 rpm, that would be the problem.
Back in 2005 if you were DaveW in a pinto car at M-O you would be running a 90 mph 1st gear, 108 mph 2nd gear, 122 mph 3rd gear, and 138mph 4th gear. (all speeds based on reading at 6900 rpm)

[Purple Frog]

From 2010 post:

OK. I called QS and asked what they do to set the valves cold.

When they set up the head on the bench, for the intakes, they use 0.010 on cylinders 1-3, and 0.009 on cyl # 4. For the exhausts they use 0.013 for # 1, and 0.012 for the rest. They might have to adjust one or two slightly hot after they're run in, but that gives them the desired 0.008 intake and 0.010 exhaust (hot).
So the 0.002 extra clearance, as I said before, seems about right for cold valve adjustments of a head mounted on a block.

[Purple Frog]

Carb issues:
Is it dumping fuel at idle (too high float level) or during cornering (need to solder shut the secondary idle jet)? Or is it some other problem?


Carb Jets:
The secondaries should be mechanically operated. This means that any time you are at full throttle (and this will be 95% of the time), both the primary and secondary will be open. If you are seeing a discontinuity in the EGT's, that may be due to the auxiliary enrichment tubes (put in by various engine builders to modify the fuel distribution) starting their flow with a slight delay - this is normal.


The main jets are located in the bottom of the float bowl. To change them you remove the top of the carb (6 screws) -- if you are careful not to tear the gasket, it can be reused. You will probably have different jets for the primary & secondary venturi -- so be careful to note what size is currently used for each one. A "one jet leaner" usually mean a differnence of 5 (i.e. change a 175 to a 170 - smaller numbers are leaner).

Your carb also has air corrector jets (aka A/C) -- you also remove the carb top to access these -- but they are located on the upward face of the carb body. Again, primary and secondary values may be different. The air correctors adjust the mixture just at the high flows (i.e. high RPMs) -- three steps of A/C jets is about the same as one step of main jets. A larger A/C jet will make the mixture leaner, and a smaller one will make it richer.

Finally, you will find idle jets on the side of the carbs in the main body, just below the top. You unscrew the holder, and the jet sits in that. Watch out not to lose the rubber o-ring under the jet holder. Idle jets are hardly ever changed, but you should pull them out to make sure a piece of debris hasn't clogged the very small orifice.

The mixture screw located near the base of the carb will adjust the mixture at idle. With the engine running at idle (usually 900 - 1000 RPMs), screw it in until the engine starts to run rough, then back it out again until the engine again begins to sound a bit rough -- at that point, screw it back in 1/4 to 1/2 turn and you're all set -- a smooth running engine.

DaveW’s jets in 2006 were:

JET PRI SEC
AIR 200 140
FUEL 135 165
(FOR AVGAS, ~55F)

[Purple Frog]

Check cam timing, you could have had a rock get in the belt and it skipped a tooth....

[Purple Frog]

A well prepared pinto race carb will do this: At idle in the paddock if you rapidly go to wide open throttle it should "stagger" a bit before it revs up. (per DaveW in 2007)

[Steve Demeter]

You mentioned that it acts up with any steering input.

I would also check the pick up in the fuel cell to make sure it is in the right position. Lateral forces could be uncovering it.

This is a long shot I know

[DanW]

You mentioned that it acts up with any steering input.

I would also check the pick up in the fuel cell to make sure it is in the right position. Lateral forces could be uncovering it.

This is a long shot I know

Or there is fuel cell foam debris blocking the pickup.

[redcar9]

What 2B said. Timing.
Plus what gear set is in the car? What rpm at 110?
With the pinto in race mode you should never get below 5500 rpm.
If you are trying to drive out of T5 at 4500 rpm, that would be the problem.
Back in 2005 if you were DaveW in a pinto car at M-O you would be running a 90 mph 1st gear, 108 mph 2nd gear, 122 mph 3rd gear, and 138mph 4th gear. (all speeds based on reading at 6900 rpm)

Thanks for all of this info, let me look at all of this.

I think the timing was around 35 or so, I had issues starting when it was at 37.
This was measured at 4000rpm

[Purple Frog]

All the pintos I've been around start very easy... like they just jump to life immediately, no long cranking. Hit the starter button... boom.

I suspect something is out of spec. A lot of what you write sounds like carb.

There were some older pinto versions, usually built by Dixon, that had distributors locked without any advance. To start them cold one sometimes would have to set them back to 10 degrees to be able start and get warmed up. Once warm then you advanced it to the race spec. It was to me a PIA.

Does this car have an MSD ignition? I've seen them go wonky.

[Rick Kirchner]

just for grins, check your fuel pressure

[Joefisherff]

just for grins, check your fuel pressure

I'm with Rick, Rex Gunning chased an issue and determined that some of the fuel pumps are designated as a higher pressure pump versus the stock pump (which could not keep up with the fuel demand of a higher performance engine, he tried an electric pump and the issue was solved.

[roadracer]

Many good suggestions and checking timing with a light would be a good step if not already done. Pertronix ignition? They will fail and can appear to be a fuel starvation issue. Problems always end up being something simple... but hard to find.

There is a small fuel filter inside the carburetor on the underside of the fuel inlet. It has a 19mm brass cap. The filter is a fine mesh and worth checking. There should be a fuel filter between the fuel cell and the fuel pump and I'm sure you've checked it.

Float level has been mentioned but important to check it after the engine has been turned over on the starter and then the fuel line to the carburetor disconnected. This step guarantees the fuel pump will not be squirting more fuel into the carb when the top is removed. Also a good time to check fuel pressure as it is typically 3-4 lbs, not 10+ as mentioned above. Fuel level in the float bowl should be 3/4 inches. The needle valve has a taper and it should not have a ridge on it that could bind up.

The fuel float (brass?) can be an issue if it is hitting the side of the carb body, so look for any bright spots where it may be touching.
Also check the float to be sure it does not have a leak by giving it a shake. The float "drop" or free-play is important and it should be 1/4 inch. With the carb top on its side and the float pivot pin up and down, the seam on the float opposite the pivot should wiggle back and forth about 1/4 inch. The brass float has a small tab on the side to restrict movement and typically they are not adjusted properly.

Underneath the air correction jets are the emulsion tubes. Using a small easy-out or length of wire they can be lifted out, tapped on a hard surface to dislodge any foreign bits. Doing one at a time makes it easier to avoid mixing up the parts. They are easy to overlook.
Lastly, both carb venturis should be tight in the bore.
Good luck with this!