Accelerator Pump Jets

June 14th, 2012

So, last October I went to Thunderhill and had some carb tuning done at MCE. They did a nice job – leaning it way out and boosting the HP and torque about 15 points each. However, once they were done, there was a big hesitation right at the beginning of accel that was really disturbing on track. I asked Scott about it, and he suggested that with it leaned out, it wasn’t getting enough gas right at the first push of the throttle, so the accelerator pump probably needed bigger jets. It’s taken me 9 or 10 months to finally get around to replacing these things! I had some in the garage already. The existing jets were 28 (primary) and 31 (secondary). I watched this video here, which gave me a great instruction on how to pick and install new ones.


I tried out 31 in front and 37 in back and took a test drive. Better! but still some hesitation. So I put a 37 in front. Great! the car is off the line like a mountain goat. I may try out 37/40 at some point, but the 40s I have are a different shape, and I don’t have the necessary drilled screw, per the video.


I’m looking forward to getting this on track again to try it out. There’s some chance of me going next weekend to Laguna. However, it’s a 90dB sound limit! I’ve been metered at 94.5 at Laguna before but then passed the 92 limit by just lifting a bit when I passed the booth. Not sure about 90. We’ll see how it shakes out!



There was still some initial lag. I took a look at the throttle action and pump actuation. I saw that not much was happening at the beginning of the throttle action, so I have moved the cam to position 2. I reset the clearance at WOT to .015. The jet seems to start much earlier now and that may be what I need. I also learned from the video that I should have the 50cc pump diaphragms in there for these .037 nozzles. Not sure if that’s what I have! I’m on the borderline though if not, so I think I’ll run this and see what happens.


Laguna Event

September 7th, 2011

Took the car to Laguna in March. Craig drove his BMW and had a great time. The track was rainy in the beginning of the day, which made for some excitement! I ended up wrong-way around after Turn 2 entrance. Thereafter, I learned to be subtle with the throttle. Rain teaches you a lot.

The car was fantastic!

More and more confident through the day, and started really getting on it after Turn 5 where the sound station is. Black flag… Came in at 94.5 dB so very close. Just backed off a little after that in that spot and the rest of the runs were fine.


oil changes

September 7th, 2011

first oil- Brad Penn break-in oil

50 miles – changed to Brad Penn straight 30 wt

500 Miles – changed to Joe Gibbs XP-1

lost a few quarts at a track event – high revs? blowby? rings not seated yet? Installed a blow-by can. nothing in it yet

2000 Miles – changed to Amsoil high zinc

About 1500 miles – changed LR axle oil seal, now need RR as well before running another event

maintenance ,

X Pipe

May 30th, 2010

I am installing a Dr Gas Crossover Pipe. This will help equalize the pressure between the 2 sides of the exhaust. This should add a bit of torque, and also quiet the exhaust down a little. I got the measurements from Scott on where exactly it needed to be (and not be) to optimize the torque curve. Amazingly, I’ve been able to nail the placement of the center of the X very close to ideal, about 35.9 inches from the ends of the primaries inside the header. This got a little interesting, because since the primaries on the left and right are different lengths, the collectors are different lengths as well.

I pulled a rookie move when I welded the center section together – I welded it all on one side and then the other. MIG gets really hot, so the metal warped a bit and threw off my nice fitment job.  I muscled it into place anyway. Hopefully that will work out.

Engine and Drivetrain, Photos , , ,

Fuel Lines

May 26th, 2010

I re-did all my fuel lines. Earlier, I described that I’d used the hard line, and then mated -6 fittings and braided line to it. Turns out I need -8 to fully supply this motor, so I re-did them all. Finding a route that stayed away from heat, was well protected, and wasn’t inside the car, was a challenge, but I think I did pretty well with it. In 2 areas, I passed the line through sheetmetal. Ordinarily, you’d do that with a bulkhead fitting. These areas would be pretty hard to reach though (if not impossible) with the car together, so tightening the fittings to solve a leak or something would be really hard. I ended up putting a rubber grommet in the sheet metal, and putting heat-shrink tubing on the fuel line. If I hadn’t put the heat-shrink on there, the line would have ended up cutting trough the rubber in time, and then cutting into the sheet metal. It might also be weakened itself, by the sheet metal rubbing on it. Combining that with mounting the line securely so that it won’t move around, makes for a pretty solid setup.

Fuel, Photos


May 26th, 2010

I ditched the old Doug Thorley headers because they wouldn’t work with my new motor. Too bad, because they were nicely made. I bought a set of Hooker Super Comp headers, part number 6111-HKR and have set about modifying them a bit. I ground out the tubes to match my heads’ exhaust ports, had the flange re-welded on the outside instead of just the inside, and am modifying the collectors.

The primaries on the left side are all within about .5″ of each other in length – impressive! On the right side, tubes 2-4 are close to each other, but a couple inches shorter than the left. Tube 1 is almost 5 inches longer than 2-4! It’s the best I can do, I guess. Hooker says they are “tuned” equal length primaries. I guess “equal” is relative. True equal length headers would cost a lot more. Tough to make.

To make up for the difference between left and right, I’m extending the collector .7″. The left-hand collector needs to be 18.2 past the ends of the primaries and the right hand needs to be 18.9. It’s not really possible to get very exact with it, because the ends of the primaries really vary (+- 1/8 or more). But, I’m getting real close.

Making the exhaust system is fun and challenging. I’m sore from lifting pipes into place over my head, fitting, removing, cutting pipe, lifting into place, etc. The headers are a real tight fit. The driver’s side one has to go in first. I have to lift the engine and move it over towards the passenger’s side in order for the pipes to clear the steering box and shock tower on the way in. Luckily I did install some Ron Morris engine mounts that allow for side to side and front to back adjustment. So, lift, move, put the header up and a couple bolts in, then shift the motor back to center and drop it. Then install the passenger’s side. It all has to be done multiple times in the fitting process.

Engine and Drivetrain, Photos , ,

Engine assembled

March 27th, 2010

Dad and I went over to Ray’s for the final engine assembly. We made a couple mistakes. First, we forgot to install the fuel pump eccentric! No matter, it forces me to go electric, which will be great. Second, we didn’t realize that htis type of lifter needs to be installed before the heads. oops. Otherwise, the assembly went great and the motor looks good.

Engine and Drivetrain

Transmission Linkage Rebuild

March 25th, 2010

One of the things about my old transmission was the sloppy shifting. Anyone who drove it could tell you,  you never really knew for sure if you’d shifted into a particular gear. Well, I bought a new Hurst Competition Plus shifter, part number 391 3180, and took it over to Ray’s. We took apart the old linkage and cut the rods to the proper lengths. Then, we threaded the ends and installed heim joints. Where new bushings were needed, Ray machined some new ones out of stainless steel on his lathe. Then, he took apart the Hurst and made shims for every gear. This process basically took out all of the slop and left me with a REALLY nice shifter.

Engine and Drivetrain, Photos ,

Repairing the Inner Fender Apron

March 25th, 2010

Fuel Filter Bracket

March 25th, 2010

My friend gave me a killer fuel filter – Mallory 3140 – but it was missing a mount bracket. I made one out of 16 gauge sheet metal.

Engine and Drivetrain, Fuel, Photos