Surging idle and hesitation at WOT

[ukemike]

Our cb7 race car is having some problems that seem like they might be a vacuum leak. It surges at idle when it is cold. At wide open throttle while driving down the road it hesitates very badly.

I have sprayed carb cleaner at all of the vacuum joints. There was no reaction. Any thoughts? Our races in three weeks.

[Raf99]

Our cb7 race car is having some problems that seem like they might be a vacuum leak. It surges at idle when it is cold. At wide open throttle while driving down the road it hesitates very badly.

I have sprayed carb cleaner at all of the vacuum joints. There was no reaction. Any thoughts? Our races in three weeks.

Gounds, distributor / wires, plugs, fuel pressure? A broken IACV wouldn't cause hesitation at WOT.

[ukemike]

Big exhaust leak?

Well there is a big exhaust leak just back of the catalytic converter. My team-mate thinks that's the cause of all of it. I'm not sure sure. Regardless we have to get that fixed. We're going to take it to a guy to have him fix it and take out the cat at the same time.

I followed Eric the Car Guys troubleshooting for rough idle and adjusted the fast idle valve like he showed. It was surging when the fans would come on (which put some load on the alternator) that surging stopped. I didn't get a chance to start it cold and see if it made a difference.

[Fleetw00d]

I followed Eric the Car Guys troubleshooting for rough idle and adjusted the fast idle valve like he showed. It was surging when the fans would come on (which put some load on the alternator) that surging stopped. I didn't get a chance to start it cold and see if it made a difference.

What was his recommendation for adjusting the FITV? Just cranking it down? The problem is that the o-ring on the light yellow piston inside the valve has taken a complete compression set and allows air to leak past the piston. This thread explains how the FITV works and has necessary information for replacing the o-ring on the piston and adjusting the valve: http://www.cb7tuner.com/vbb/showthread.php?t=206012

[Raf99]

Well there is a big exhaust leak just back of the catalytic converter. My team-mate thinks that's the cause of all of it. I'm not sure sure. Regardless we have to get that fixed. We're going to take it to a guy to have him fix it and take out the cat at the same time.

I followed Eric the Car Guys troubleshooting for rough idle and adjusted the fast idle valve like he showed. It was surging when the fans would come on (which put some load on the alternator) that surging stopped. I didn't get a chance to start it cold and see if it made a difference.

If the leak is past the CAT i wouldn't worry about it. But sounds like you have multiple things to check...

[ukemike]

Cap and Rotor

When I said earlier that there was an exhaust leak I was understating it a bit. The exhaust had actually broken just behind the cat. We took it to a local muffler guy who also races in Lemons and asked him to cut out the cat and patch it up with whatever scrap he had around. We also had him reinforce the lower front frame bit that has out tow bar bolted into it.

Mitch, the muffler guy, did not do what we asked. He did the reinforcement just like we asked. But with the exhuast, he cut out the cat and gave us new 2" pipe all the way back to the muffler (which is a glasspack). He remounted the muffler straighter and moved it inboard a bit to minimize damage if we get rear-ended. I'm not a believer in bigger exhuast = better. I know that if you go too big the exhaust can cool and slow down and flow worse. But after the fact I found that 2" is not out of range for this motor.

It does sound good.

So my new cap, rotor, and plugs arrived thursday. I put them all in and that was the source of the WOT issues. The contacts in the cap did not look good at all. The plugs were old. I used the oem nkg copper plugs. They are cheap, I'm just going to check them after two races then pick a reasonable replacement schedule based on mu observations then.

Took it for a spin around the block and it runs fine again. BUT the battery light was still on. I noticed that earlier when the idle was acting up. It definitely wasn't on at our last race. So I got out the multi-meter. Voltage on the battery was 12.45. That's a bit low. Running, voltage was still 12.45 at the battery and comming out of the alternator. I put the leads on the battery and let it run for 15 minutes or so. Voltage dropped to 12.38. Revving it up did not cause the voltage to go up. Sad. A new alternator is not in my budget, and it has to get fixed now. Race is saturday. The alternator guys in Berkeley are closed on the weekend, so NAPA auto in San Rafael, here I come.


The idle issue seemed solved after adjusting the fast idle valve and was acting fine when I dropped it off.