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Keihin CVK34 carb set up

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Al
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Re: Keihin CVK34 carb set up

#31 PostAuthor: Al » Sun Sep 12, 2021 12:27 pm

Intermittent yellow coughs are the pre-cursor to full yellow and for myself, that's about where i back mine off to after witnessing full yellow. The fact that you cant see full yellow.... dont know. You may be able to simulate a more rich condition by either using an old blocked air filter or restricting the air flow into the air box with youre hand /bit of rag, just for colour tune testing. Using a little choke may do the same. You can test the chokes using the vacuum gauges with a cold engine and it will highlight any that are not closing sufficiently although that doesnt appear to be youre problem.
I was going to ask where (what country) youre carbs are from, but looking at CMSNL and the different models for different markets; France / Europe / USA, it seems that they all use the same #35 pilot jet so its not as if its been lean'd off for environmental reasons!
I take it that there are no issues with throttle return springs and that it has enough advance?
Did you strip all the bodies of jets etc when they were US cleaned?
What air filter are you using and what octane rating is the fuel you have been putting through it?
I'd be interested to know what you see from running the pilot air jets opened out beyond 2 3/4 turns. If at perhaps; 4 turns out, you see no difference in the colourtune then that suggests that there is still a partial restriction in the pilot circuit!

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Re: Keihin CVK34 carb set up

#32 PostAuthor: moizeau » Tue Sep 21, 2021 2:23 pm

Thanks Al. Yep it's on #35 pilots. When the carbs were US'd they still had the pilot jets in, the rest was completely stripped. The reason they were in was that I was fearful of buggering the head of the jets, they were that tight, and thus ending up with 4 scrap carb bodies. The chap removed them while they were still warm after the US with a better fitting screwdriver than I have, then jet filed the pilot jet and carb cleaned and compressed air the passage way.
I blocked the clean air pipe from no 4 and put a stopper from my ST carb over the inlet rubber nipple just to take that out of the equation. Started it, warmed it, kept unscrewing the pilot jet slowly until it fell out........still blue. Carbs off again then.
While I was in the UK last week I was talking to a chap about it who cleaned some speedboat carbs. After having a nightmare and wrecking a bank of carbs trying to clean them he got another set and before he US'd them another chap who works on carbs all the time advised him to put each stripped carb body into a sealed glass jar full of petrol or meths, then put the jar in the US. Apparently the gains are 2 fold. Petrol is a better cleaner than the US solution and secondly all the shite that falls out stays in the jar and doesn't contaminate the US solution. The carbs when they came out were squeaky clean and ran great.
Has anyone else heard of or tried this?
I forgot to try blocking the inlet air to change the fuel / air ratio (for test purposes), will do this before the carbs come off.
Thanks again

EDIT, just blocked the air inlet to the filter box, full yellow. Tried adjusting number one this time, can get a full yellow and a correct blue....the full yellow was at 4 1/2 turns, correct at 4.
Pete

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Re: Keihin CVK34 carb set up

#33 PostAuthor: Al » Wed Sep 22, 2021 9:50 pm

EDIT, just blocked the air inlet to the filter box, full yellow. Tried adjusting number one this time, can get a full yellow and a correct blue....the full yellow was at 4 1/2 turns, correct at 4.


Just to be clear; you are saying that you could ONLY witness a yellow flame WITH a restriction to the airflow into the airbox AND that was with the pilot fuel screws at 4 1/2 turns out from lightly seated?
If that is the case i am out of ideas'. Re-visiting the fuel levels (now VS what you started with) it may be necessary to raise the levels a little to make more fuel available to the pilot circuit. I would imagine in the normal course of events that the fuel level will rise with time as components bed in or wear in / out and that when its had a few thousand miles the scouring effect of fuel through the pilots may remove any furring or scale. Though you did say the US guy polished them out. That may be the long game if you can live with it till then.
Normally at this point i turn to violence :D It has its place, and i normally snip a bristle from my wire brush and go after the tiny orifice in the carb mouth where the pilot fuel screw's delivery emerges. I have never had any luck with compressed air blowing from the mouth of the carb at that point and the pilot fuel screw removed.
I had a look at the Dynojet stage 1 for the zephyr. Interested to see that very little gets changed but they do recommend setting the pilot fuel screw to 2 1/2 turns out from lightly seated so i am guessing its a known quantity.
Whats next :?:

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Re: Keihin CVK34 carb set up

#34 PostAuthor: moizeau » Thu Sep 23, 2021 4:27 pm

Cheers Al. I could get a solid yellow burn by restricting the air. Only confirmed on no. 1 and 4 because the tank was still on. Without a restriction I couldn't get anything apart from blue on No. 4 but could get full yellow at 4 1/2 turns out on No. 1 . 4 turns gave the correct colour.
I had a dynojet kit on my old Zeph (Only did a stage one). It came with a drill bit for the slides, replacement needles and 2 sets of mains, 1 set for standard pipes and a larger set for aftermarket.
I'm going to whip the tank off and see what the middle cylinders are doing first. If I can get the correct burn, (irrespective of turns out) on 3 cylinders I may live with it for a while then check again in a few hundred miles. If not I'll strip the buggers again (this time with the pilot jet removed as well) and give then back the US chap. He said last time If they weren't right he's chuck 'em back in. Just looking for some large enough jars to stick them in and fill them with petrol.
I'm running 98 E5 but have only done 40km testing, who knows what the previous owner used, probably 95 E10.
Pete

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Re: Keihin CVK34 carb set up

#35 PostAuthor: moizeau » Mon Jan 03, 2022 11:21 pm

Thought I'd updated this, obviously not.
Put the colortune back in the box and went old school. Fastest tick over on each carb. The screws are way off where they should be put it starts, doesn't pop, ticks over on choke and when warm and doesn't stall after a blat down the road. Not very chuggy at all from low revs (1500) in a high gear. Will run it as is for a bit then have another play with the carbs when they've been flushed through.
Thanks Al for all the guidance.
Pete


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