Wednesday, November 16, 2022

Kiss my Keyster goodbye…. the Frankenbike 350 story continues

I have commented on the quality of the Keyster brand of motorcycle carburetor kits for years now, and am joined by many others who have suffered from the lack of accuracy of their components. I generally spend my repair time with 250-305 twins, but occasionally I have to work on bikes from a later vintage, often times 350 twins and an array of four-cylinder models. The challenge is that Keyster is one of the few remaining companies that make an attempt at offering repair kits for vintage motorcycles of all brands. 

You would think that a company that goes to the trouble of manufacturing carb components would have the expertise in duplicating the original parts accurately, but that is often not the case. We have found that the slide needles for the CB77 kits are too rich for Super Hawks, but work okay for Scramblers, which use a different needle taper. Likewise, all of their bowl gaskets are too wide where they fit into the forward slot in the carb base and don’t take into account that there are two little bumps that need clearance.

In recent years, the kits for the 305 Dreams started coming with #130 main jets which are way too rich for a stock bike that came with #120 main jets from the factory. Every time someone contacts me about difficulties with plug fouling on a Dream, the first question from me is: Does it have a Keyster kit installed with a #130 main jet? Often, lately, that is the answer to the problem. Early Honda models have JIS thread pitch jets, so you can’t plug in the later versions which are ISO pitch now. One of my suppliers does supply JIS main jets, separately from whole kits.

Usually, the plan is to reuse any OEM hardware pieces like jets and needles. I have discovered that the dimensions of the Keyster float valves are a little off, as well, causing the need to bend the float tang excessively to get the float height to be correct.

If you read my recent blog post

which was supposed to have been published back in September, you can see what kinds of problems can occur when you are using aftermarket components, like Keyster carb kits. Well, the story didn’t end there after all.

After a few days of happy driving, the bike became difficult to start and would stall out after a few seconds. I shared as much guidance as I could over text messages with the owner, but despite his best efforts the bike refused to come alive again. Part of the difficulty is that the bike is 30 miles away in Leucadia near my sister’s home. I only go up there about once a month for my nearby chiropractor’s appointment so I had hoped to be able to resolve the problems via text messaging. This was not the case, but my next appointment came due so I packed up tools and equipment to do a house call after my appointment.

Having tools on hand proved fortunate as my chiropractor needed some carb cleaning work on his Vespa Scooter, so I was able to trade services and save $125 for the visit. After that work, I drove down the road to the awaiting CB350 Frankenbike and its frustrated owner. Let the fun begin again….

Checking for battery voltage first, I measured 12.4v so that was a good starting point. The bike would try to start, then die as soon as the throttle was turned at all. There was backfiring going on during the startup attempt too, so that is generally an air leak or incorrect ignition timing. It was apparent that the right side cylinder was misfiring and not really catching on, so I focused on that side first. 

One of the other problems facing the owner was that the throttle cables wouldn’t synch up properly, which was eventually resolved after the carb cable extension to the left side had slipped out of the junction, leaving uneven lengths. The aftermarket cables have big fat junctions, unlike the originals, which can get trapped beneath the fuel tanks when the tank is set back on its mounts. The second problem was that either the threads in the carburetor cable holders were stripped or the cable end dimensions were undersized so that you can’t tighten the cable adjusters onto the carburetors. After a lot of fiddling, I got them as close as possible to matching each other and left it at that.

With the point cover off, the left side points didn’t seem to be opening very far which resulted in retarded ignition timing. The point adjustment was all the way open and the point backing plate was rotated as far as it could go but still, the timing was 20 degrees retarded, which explained the backfiring on that side. Eventually, I had to bend the point base contact outwards to get some point gap established and corrected the ignition timing. The bike started up and kept running but the right side wasn’t taking the throttle off idle, but it was idling okay. I thought perhaps the carb diaphragm was damaged, so removed the carburetor and pulled the top off to inspect the diaphragm. It looked fine but THE SLIDE NEEDLE WAS SEPARATED AGAIN! I don’t think that Honda’s Keihin carburetor slide needles are made in two pieces, but these certainly were. I tried to crimp the end of the needle slightly to make an interference fit with the little top hat end and tapped it back together again. It seems to be secure for the moment, but I don’t trust it at all now.

The bike started back up and was running on both sides, but idle mixture settings were off specs and there was still hard starting and some backfiring going on. I hit the intake manifolds with a blast of brake cleaner which I had brought along and the RPMs jumped instantly. A closer look at the manifolds revealed that the paper gaskets that were supposed to seal the manifolds to the head were blown out causing a huge air leak. The nearby Auto-Zone was a source for a tiny $6 tube of high temp RTV gasket sealer and the manifolds were glued back onto the cylinder head, solving that problem.

I had been on the job for more than 2 hours, improvising repairs and troubleshooting but finally had a functioning motorcycle, at least at the moment. I feel like starting a GoFundMe page for my suffering friend who still is sleeping in his car, next to the railroad tracks, living day to day from his meager income from photography work in the local area. He goes out and shoots local surfers in action, plus has other photography gigs in the county, but it isn’t enough to really get him settled into an apartment where the mean rent prices are in the $2k range. Surprisingly, he’s adapted to his situation the best he can for now, with a hopeful attitude for future work and a warm spot to call his own. See his work at 

I’ve done what I can do for the Frankenbike 350 for now. It needs a whole host of OEM parts to get its reliability improved, but it is what it is at the moment.

Bill Silver aka MrHonda


1 comment:

  1. Wow! This was quite the story Bill! But if anyone could get that bike back on the road, it was you. Feel proud that through all your posts here plus your repair manuals, I have learned a ton about these old Hondas and how to diagnose troubles. My '62 250 Dream(purchased with 7k original miles) recently started making strange top end noises at WOT. I scratched my head over it because it ran perfectly. After much thought, I figured perhaps the original head gasket from 1962 was shot so I dropped the engine and removed the head and sure enough, it was completely shot plus the oil o rings to the top end leaked oil into the cylinders, not out from the front of the engine as usual. Fresh OEM gaskets and she's back on the road as sassy as ever. I didn't even bother pulling up the cylinders because who knows what ring set I'd need on this old girl and it ran great with a blown head gasket. Your book came in handy once again as I buttoned everything up. Thanks again Bill for what you do!