steve91tt

The o-ring is close to the outside of the manifold so the porting does not effect things. Here is a photo of the RTV smear in the notch I'm referring to. Not the neatest job of applying the RTV but at least it got me on the track. I'll tidy it up later. Todd at Wolfe creek racing pointed me at the solution. I think the timing was 75% of the solution. Vacuum leak was the other 25%.

A quick update on my Mikuni issue. I ended up having a small set of vacuum leaks around my carb/manifold o-rings. The o-ring comes quite close to the edge of the outside surface of the canon manifold in one spot on every runner. I added a small dab of RTV in that area. I also rechecked the timing and found that it was 5 degrees lower than it should have been! Not sure how it got that way but I fixed it and now she idles fine. I ran a time trial event last week at the local track and it performed flawlessly. Thanks for all the help everyone!

I'm using the stock timing curve because I using this setup on my track car which lives it life between 3000 and 7500 RPM. Solid, stead and reliable 34° of maximum advance is all I care about. If you are looking at the 280Z dizzy you might consider the 75/76 model as it uses a magnetic pickup and when coupled with an MSD box it does not require an extra ignition module as the later model units do. Dave Rebello recommended this setup to me and talked me out of going with a crank trigger system. In his opinion it's the most reliable ignition setup for my application.

I recently swapped out my Mallory distributor for a rebuilt stock dizzy from a 1976 280Z. The stock 1976 unit can be used to directly trigger the magnetic pickup on a MSD box. I've thus far been very happy with the results. Other than the MSD box this system should provide OEM reliability and if you go with the programmable MSD box then you should have the flexibility you are looking for. Not as sexy as as trigger wheel setup but performance should be the same or maybe a little better due to the higher voltage and multiple sparks provided by the MSD box. Just my $0.02.

I checked the valve lash a couple of months ago. All was good no adjustment needed. AFR is in the 11's at idle. I can't drive the car right now as I took the rear stub axel off this morning to replace a grumbly bearing. Should have it back on the road for a test drive on Wednesday.

I checked the float levels by removing a jet block from each carb. The float levels look normal and even between carbs. I would also expect that if the floats were to blame that pairs of cylinders would misbehave as one float adjustment services two cylinders. I re-torqued all the bolts and the car still backfired. I then started turning the idle mixture screws to richen up the cylinders that were popping and lean out the ones that weren't. With this adjustment the popping/backfiring has stopped. I ended up with the following mixture adjustments per cylinder. 1 = 1.75 turns out 2 = 1.25 turns out 3 = 1.25 turns out 4 = 2.0 turns out 5 = 2.0 turns out 6 = 2.5 turns out I assume that the extra fuel requirements of some cylinders is a function of a specific vacuum leak in that cylinder and potentially carb to cab differences in the idle fuel system. This is a bandaide solution for some underlieing problem(s). The search continues.

I've tried flowing propane, carb cleaner and water around the flanges with the engine running to no effect. I'm not sure how to find the leaks.

I re-tightened the manifold/exhaust bolts last night to no effect. Last night the car was backfiring though 1, 4 and 6. This morning I removed the manifold and exhaust and replaced the gasket with a felpro unit applied dry. I had a new set of exhaust and intake studs laying around so I replaced them while I was there. The car now seems to idle more roughly than it did before the gasket replacement and it pops quite badly though #4 and #6. The backfires are now more intense than they were. I plan to let the car cool and re torque the gasket. Any advice for getting the intake to seal?

I opened up the float chamber to adjust the floats. I used new gaskets when I reassembled them.

Yes and I replaced the o rings with new. The previous owner had done a hack job on the carb side of the intake. The head side is still stock dimensions. This is a photo from before porting the carb side of the intake... 90% done... I didn't take a photo of the finished product but it made for a nice smooth transition from the carb to the plastic spacer to the manifold if you look down the throat of the carb.

I took the carbs off the intake, the intake off the head and I took the top off the float chamber. I smoothed out the transition from the carbs to the manifold. I did not do anything with the head side of the manifold.

Backfiring out of multiple carb throats. I'll have to double check to see if I left some parts on the bench.

I took my Mikuni 44's apart this weekend to gasket match the cannon intake. The car now backfires quite badly out of both the carbs and the tailpipe while idling, downshifting and cruising. The AFR's are 11-12 while backfiring and the car pulls hard at WOT where the AFR is in the 12's . The plugs seem normal, timing looks normal, float bowl levels look normal and compression is 170+/-5 across all cylinders. The engine is a Rebello L30. The carbs have 39mm chokes, 150 fuels, 180 airs and deleted balance tube on the intake. Any advice as to how I should diagnose the problem? Could this be caused by a vacuum leak?

I run a BRUTE POWER / PERFECTION CLUTCH 92016B clutch in both my cars. Cheap and indestructible. I've got +6000 track miles on my Rebello powered track car and it's still going strong. I paid less than $80 for the kit which includes a bearing, bushing, collar and clutch.