PPMPR: Project Poor Man’s Pro Race

[toratora]

All of the carbs I've worked with that have an idle mixture adjustment in that position (behind the slide) are air-bleeds. That would agree with my theory about the vacuum leak (hanging idle, best with screw all the way in).

As far as the Main Jet size, how was it running out on the road at WOT?

I agree it’s weird, but as you can see from the docs posted above, turning the screw out enriches the mixture.

For the most part the bike is running quite good. It is a bit on the rich side, as is backed up by the wash. I need to find those pilot jets, and then get at the carb.

Still I’m really happy that changing out the CDI had such a positive effect on the bike. The possibility is still there that with an appropriate CDI with the right curve the engine could be woken up just a bit earlier. If it could be tuned to get on the pipe at around 8K it would make the bike very easy to ride fast—that was the expectation of running the HPI on the Silver bike.

[jkv357]

I agree it’s weird, but as you can see from the docs posted above, turning the screw out enriches the mixture.

For the most part the bike is running quite good. It is a bit on the rich side, as is backed up by the wash. I need to find those pilot jets, and then get at the carb.

Still I’m really happy that changing out the CDI had such a positive effect on the bike. The possibility is still there that with an appropriate CDI with the right curve the engine could be woken up just a bit earlier. If it could be tuned to get on the pipe at around 8K it would make the bike very easy to ride fast—that was the expectation of running the HPI on the Silver bike.

You mean the Keihin doc? I wouldn't go by that. That's not even standard for all Keihin carbs. I've had Keihin carbs on single cylinder engines that have been both ways. A fuel-bleed is normally near the floatbowl or in front of the slide.

I didn't think your carb was a Keihin.

[toratora]

You mean the Keihin doc? I wouldn’t go by that. That's not even standard for all Keihin carbs. I’ve had Keihin carbs on single cylinder engines that have been both ways. A fuel-bleed is normally near the floatbowl or in front of the slide.

I didn't think your carb was a Keihin.

Yes, the MetraKit carb is a copy of that particular Keihin PWK, so expectations are that it will function in the same manner. Yesterday I did find the slow jets. Just have to wait for some clear weather to try them.

[jkv357]

Have you found anyone that can give you a definitive answer as to the type of idle mixture adjustment that carb has?

[toratora]

Have you found anyone that can give you a definitive answer as to the type of idle mixture adjustment that carb has?

Not really, I just have to go with the PWK documentation. Here’s what they have to say about it on their website:

Air/gasoline adjustment screw
The carburetor pictured in the exploded view uses an air adjustment screw (#5 in illus.) in that it is located upstream of the throttle valve (slide) and meters air; turning it counter-clockwise leans the mixture off idle.

Some carburetors have this screw located downstream of the throttle valve, in this case the screw meters fuel and opening this screw results in a richer mixture. The idle mixture screw usually has a range of one to two turns out from fully closed. If you need to adjust above or below this range then the slow jet will probably need to be replaced with one richer or leaner as required, consult your owners manual for the standard setting.

[jkv357]

Air/gasoline adjustment screw
The carburetor pictured in the exploded view uses an air adjustment screw (#5 in illus.) in that it is located upstream of the throttle valve (slide) and meters air; turning it counter-clockwise (OUT) leans the mixture off idle.

Some carburetors have this screw located downstream of the throttle valve, in this case the screw meters fuel and opening this screw results in a richer mixture. The idle mixture screw usually has a range of one to two turns out from fully closed. If you need to adjust above or below this range then the slow jet will probably need to be replaced with one richer or leaner as required, consult your owners manual for the standard setting.

That would confirm it is an air bleed, and turning it IN reduces the air flow and richens the mixture.

When in doubt, I've always found that if the adjustment is behind the slide (on the side closer to the air filter) it's an air bleed.

[toratora]

The documentation is most certainly in conflict with itself, and your logic seems to prevail. So moving forward I will think of it as you have described! Thanks for taking the time and effort!

[toratora]

It was time to play with the pilot jet. There was a 45 pilot in the MetraKit 24mm PWK. The closest jet that I had for it was a 38, so that’s what I put in. Buttoned it up, attempted to set the air screw. The bike didn’t really want to run un less it was either all the way in, or at a half turn out. The RPMs did appear to come up a little with the half turn out, but it was hard to tell.


With a test ride the bike seemed to perform much better mid throttle. The carb is still hanging at high RPM for a while, but it seemed to be slightly better, and would come down faster with a quick turn of the throttle. I’m going to have to look at the wash to see how it looks. The main jet is probably still a bit rich.


Over all the bike is running a lot better now than before with the Red Box. It is still difficult to get it off the line without giving it a lot of RPM. I’d really like to gear it up to a front 15, but it is so persnickety off the line that it might not be a good idea. Once on the pipe the bike takes off. It’s just getting it there kind of sucks.

On the test ride there was some dude with a big four stroke waiting at a light as I pulled up to the white line. When the light changed green I had to kind of gas the bike to get it off the line because we were on a hill. The four stroke took it as a challenge, and opened it up. I was already going for it so I just let the bike continue. Mr. Four Stroke couldn’t over take me before the next light. That was interesting!

[toratora]

. It was too cold and nasty out today with the threat of rain. Therefore no outside wrenching was possible. Tuesday T-Mobile has specials, and for today they worked out a deal with Pizza Hut. There seemed to be just enough window in the weather to make a dash for pizza.

I don’t usually go for the Cinnabon action. That was included in the deal. They are tasty!


To carry the pizza home I place it on the top of the tank. It sits there nicely during the ride. I've done this many times. However, I should probably invest in a thermal pizza bag to keep it warm.

[toratora]

Last month I put in an order for some faring bolts for the RS and the GPRs. The RS employs an M5 faring bolt, and the GPRs employs an M6 faring bolt. The RS bolts showed up much faster, and the M6 bolts showed up today.

The quality looks pretty good. The bolt is actually aluminum, and these came with a nylon washer to protect the plastics. The shape of the bolt. is more of an inverted profile like on the Ducati faring bolts than the half moon Derbi style bolt, but that’s okay.

I ordered three sets of ten which should button up a number of bikes. If they work out I’ll likely order some more as the faring bolts have been one of the few fasteners I’ve not been able to source from the Bolt Depot.