Should I do a test and tune or fix this issue?

[sevenracer]

I run an IT7 car, and I am planning to run a test and tune on Friday (9/9), but I am concerned about my carb.

The carb has been installed on multiple motors/intake mani's and it never idles well. typically I can't get it to idle at all below 2000 rpm. I have run the car once with this carb/motor combo, and it ran great until I had to pull off due to losing coolant through a loose hose connection. The motor saw about 240 degrees and seems to be OK. Before I lost the coolant I was seeing about 180 deg water and 230 oil.

The other night, I noticed that the header pipes were glowing a dull red - in a shop with so-so lighting. This was while the car was idling at about 2k rpm.

I'm concerned that the car may be running lean because of a vacuum leak, and I may be risking my motor if I run it this way. But I don't know that it's not normal to have a dull red glow at the headers. It also, doesn't seem too unreasonable to think that a vacuum leak that messes up the idle circuit won't matter much at high rpm's when the primary and secondary circuits are in play. Unfortunately, I don't have EGT or A/F gauges or a known good carb.

Can anyone offer any help on this?

Thanks,
Neil

[lateapex911]

Well, Aircraft Spruce is a good source for EGT guages. Get a single guage with two needles and two sensors and make sure it reads up to about 1600 or 1900 F.

It should run about $150. Then drill your header, and clamp them on. Get the thin sensors with the hose clamp fasteners. You may have to weld a bung on the header for the sensor to seat.

Once you have that, you'll know where you stand EGT wise, and it is a cheap dyno tuning tool.

That said, your idle issue could be a vacuum leak, as you mentioned. A good way to find it is to spray a fluid like ether or carb cleaner in various locations and see if the idle picks up. Adjust it as low as it will run to start with. Try the obvious areas like the base gasket and the myriad of unused hose connections, and try sone around the throttle shaft bushing, front and back as well. Also, these cars always have a bunch of epoxied or blocked off device holes that could be problematic too, so spray them. Don't forget the brake booster hose.

Also, if you can borrow one of those cool infra red temp sensor guns, you can check out which rotor is running hotter, which is another clue.

I have a neighbors who calls the police long before my car is warm enough to even settle into an idle, so I have never let it just idle, and therefor have no idea of the proper header glow rate.

Finally, www.yawpower.com has more info about the Nikki carb than most of us can remember, so it is recommended reading. Paul tells me that demand has dropped so he is no longer providing the carb modification service.

End of an era?

[sevenracer]

Thanks,

I'll be getting EGT soon, just not by tomorrow. I think I can get my hands on an IR gun, so I'll probably try that out.

I'll probably run the T&T since my race water and oil temps were fine with this carb.

-Neil

Originally posted by lateapex911@Sep 8 2005, 05:17 AM
Well, Aircraft Spruce is a good source for EGT guages. Get a single guage with two needles and two sensors and make sure it reads up to about 1600 or 1900 F.

It should run about $150. Then drill your header, and clamp them on. Get the thin sensors with the hose clamp fasteners. You may have to weld a bung on the header for the sensor to seat.

Once you have that, you'll know where you stand EGT wise, and it is a cheap dyno tuning tool.

That said, your idle issue could be a vacuum leak, as you mentioned. A good way to find it is to spray a fluid like ether or carb cleaner in various locations and see if the idle picks up. Adjust it as low as it will run to start with. Try the obvious areas like the base gasket and the myriad of unused hose connections, and try sone around the throttle shaft bushing, front and back as well. Also, these cars always have a bunch of epoxied or blocked off device holes that could be problematic too, so spray them. Don't forget the brake booster hose.

Also, if you can borrow one of those cool infra red temp sensor guns, you can check out which rotor is running hotter, which is another clue.

I have a neighbors who calls the police long before my car is warm enough to even settle into an idle, so I have never let it just idle, and therefor have no idea of the proper header glow rate.

Finally, www.yawpower.com has more info about the Nikki carb than most of us can remember, so it is recommended reading. Paul tells me that demand has dropped so he is no longer providing the carb modification service.

End of an era?

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[Speed Raycer]

Another thing to look for is a cracked intake manifold. I once cracked my intake after swapping exhaust gaskets and not realizing that the exhaust gasket was a different year when I torqued down the intake manifold.

My header was very red, but maybe you've got a smaller crack.