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carburetor cleaning and rebuild


By superwesman - Posted on 17 November 2010

Last night I went back to the garage to get the rotor off of my 750 and had no luck so I dove back in to the 350 rebuild. I did some minor bodywork removal, attacked the tack weld on my gear shifter and use chem-dip to clean one of my carburetors.

Right after I gave up on the 750, I dunked my large carburetor parts into some berryman chem-dip. I had already sprayed the smaller bits (screws, etc.) with WD40 and scrubbed them with paper towels, toothpicks, a scratchy green sponge and my fingernails to get them as clean as possible. The tops of both carburetors show strange scratches in the chrome. It's almost as if they were struck by flying stones (which is possible). I'm going to leave them alone for now, but it would be sweet to get them re-plated.

I took off the rear fender and the rear turn signals and went to town on the tack weld that is holding my gear shifter into place with my dremel. Unfortunately, after I got through most of the weld, the dremel died. It has done this before back when I was using it with a router attachment and I burned out the motor (which was repaired under warranty!). I popped the battery out then back in and it fired up fine, but would die after a few seconds of grinding. I had also chewed threw the bulk of the grinding wheel so I put it on the charger and gave it a rest for the night. I should be able to get through it in one more attempt.

At this point, I took the carburetor parts out of the chem-dip and inspected them. I'll just say that chem-dip is not the magical wonder-stuff I had been lead to believe. There was still a lot of grime in the nooks and crannies. I had really been hoping that the chem-dip would just eat away at that stuff, but it didn't. I wiped the parts down and removed what I could using the napkins at the garage (since that roll of paper towels I had disappeared in a matter of hours).

While I was cleaning these, I had a long chat with Benjamin about jets. We looked through the blow up of the carburetor in the Haynes manual and I explained some of my performance issues. Specifically, if I put the bike to 7,000 RPM it runs fine, but as soon as I go over that mark, the engine starts to make "choppy" noises and I get immediate performance degradation. Our conclusion was that my high-speed jet needed to be up-sized to reflect the aftermarket air filters and exhaust pipes. This jet is a 105 and he suggested that I get a pair of 110 and a pair of 115 so that I could go up twice if it was required. I looked at the rebuild kit I ordered and found that the high-speed jet is a 115 so I'm going to put that in and hold off on getting the 110 until I get a chance to take it out on the highway next season.

After cleaning up the garage, I headed home with my carburetors and tools, cracked open a few beers and cleaned the hell out of the disassembled one using Q-tips. I watched half of season 1 of 30 rock while doing this and got it pretty damn clean. Then I started reassembling it. In hindsight the chem-dip actually did do a decent job. I couldn't tell in the garage, but when I compared it to the dirty one at home under bright lights, there is a noticeable difference.

I'm expecting my rebuild kit any day now so I left the float bowl off so I'll be able to pop in the new pieces, but I got the inlet and outlet "gates" back together. I used the assembled carburetor as a reference to make sure I could get this one back together properly which worked well except for the outlet gate. On the left carburetor, this gate has some printing on it (something like "K 133" if memory serves) and I oriented the gate in the same way on the right but it wouldn't close all the way. I ended up flipping it and now the two seem to fit similarly. When I started this project, I told myself I was going to take pictures of anything I disassembled and I have not been doing that and this is the first time I've been burned by it so I need to start doing that consistently. The second time I got burned happened a few seconds later when I realized that I have a little plastic o-ring that I have no idea where to put. I'm hoping that I'll discover its home while disassembling the left carburetor.

The one part that gave me considerable trouble is the groove that holds the home-plate-shaped gasket on the float bowl. The gasket was stuck to the float bowl and when I peeled it out, a residue was left behind. I scraped away at this with toothpicks and soaked it in WD40 but there's still some left. I'm going to give it another go before putting in the gasket.

I took a few pieces off the left carburetor to aid in the reassembly but it is still mostly together. I'm going to do this the slow way. Once I get the rebuild kit, I'm going to fix up the right carburetor as I disassemble the left one. Then I'll take those parts to the garage, chem-dip them and reassemble it from memory.

My last item for this post relates to my rear sets. I did some more research on my options. I'm still hoping to find a set from a CBR900RR but I have a plan b which is to splurge and get a Raask set. The issue with the CBR900RR pegs is that (as far as I can tell) some models have the gear shift lever mounted to the peg and others have it mounted to the engine. While poking around on the internet, I did see one "clever" solution where the builder had flipped his gear shifter lever so that it pointed backwards instead of forward! It's quite a simple solution with the added bonus/unfortunate side effect of setting up a racing gear shift pattern. I'm off now to look at the parts fiche for the CBR900RR to see what I can learn!