'82 Seca 400 hard starting when cold


XS400 Enthusiast
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Baltimore, MD USA
Now that the weather is better, its driveway mechanic season again lol, so back into the Seca. One of the last bugs is the bike is essentially impossible to start without bottle feeding when its been sitting for a while. Clearly the enrichener isn't pulling gas when cold, though it clearly does once the engine is running. To start it I shoot a few cc's of gas into the fuel petcock vacuum line, then crank with throttle until the engine starts turning over. Generally once its idling then it will pick up fine, and once warmed up or at least recently started, then it cranks and runs right off without any problems... just when its been sitting for a while.

I know the bowls are filling properly (have checked the drains), and a got the float level correct as per the manual (via the external transparent tube test).

I have the carbs out again (going to fix a mangled A/F screw head and get those adjustment holes properly bored out).

I noticed the ends of the enrichener pickup tubes in the bowls are very near the fill level of the gas.. I was wondering could the difficult starting be due to them not being sufficiently immersed in the gas- so the engine vacuum can't pull gas up into them?
Might have found it...

My carbs don't exactly match those shown in the 82 RJ manual- the carb is generally the same but has extra stuff; there is a tube connected to the enrichener circuit which projects down from the carb body into a well cut into the bowl itself. The well connects down to a port near the bottom of the bowl. The tube projects through a hole in the gasket put there for it.

Having looked at the bowls and identified the passage I probed with a drill and found both solidly packed with the usual sort of residue. I cleared both and will test out the carbs tomorrow afternoon- here's hoping this fixes the hard starting when cold problem :)
Good find. When I cleaned my carbs, I had similar issues. On my third attempt, I used a single strand of multi-strand copper wire to ream out all the little passages and jets. It made a huge difference over just spraying them out, especially the pilot jet.
I've had good luck with the copper wire thing too. These passages were hard packed- the crud was so solid I was worried I was drilling metal but kept going because no metal chips came out, I even felt the drill break thru the clogs. All the other passages were clear, go figure... I suppose its a lesson about what gas sitting for a long time in a carburetor can do.

When I got the bike the bowls were a little dirty but not caked with ancient crud, so I'm wondering if they had been clogged for a long time leading to the bike sitting dead, because it wouldn't start.

Fiends at Mikuni putting fuel circuits in the walls of the bowls! :laugh:
Yep that was the problem- with those passages cleared out the bike started right up no cold start fuelling issue- full enrichener puts a lot of gas into the engine no doubt. I'll bet those passages clogged over time so the bike wouldn't start and thats why they parked it. Definitely something to check when the carbs are off the bike...
My 78 is a cold blooded beast. Unless it's over 80 deg F, I always have to use full enrich to get her fired, let it run 2 minutes or so before going to the 1/2 enriched setting, then at least another minute or so before it can go off. On really cold days, I start riding on the 1/2 setting through my neighborhood.
Nice- that sounds familiar, my old Bandit had similar tendencies- it got better after a rejet but it was crazy lean from the factory. The XS gives less of an impression of over-lean. Not enough testing yet but it does look like full-enrichener might be more than what the bike likes- I had the engine fire and run at somewhere towards the middle. Experimenting while the bike was running, it was difficult to keep the engine running with full enrichener. Having gotten the AF screws properly accessible I have them both at 2.5 turns out and carbs balanced I'm inclined to leave them as-is at this point.