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Post by ccvogel on Jul 23, 2006 12:36:32 GMT -5
Just modified my 81 SR500 with the Thumper Stuff 36mm Mikuni conversion kit and White Bros repro head pipe, and a replica Dunstall muffler that I modified to fit. Most aspects of my ongoing carburation problems have been solved, but I am having one problem with the new setup. The bike takes 5 - 6 kicks to start when cold. It does not require, nor will it tolerate, any "choke," although with the weather here in Los Angeles at 75 - 80 deg F, perhaps that's normal. I'm wondering if it's possible that the pilot jet is too rich?
Any suggestions for troubleshooting?
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Post by StewRoss on Jul 24, 2006 5:16:57 GMT -5
Hi, I would guess that the carb kit comes 'roughly' correctly jetted for the SR? Try turning the mixture screw in and then out slowly to see if there is a point at which the revs peak and then begin to drop off again....adjust the engine idle up a bit first...don't screw the screw in hard to the stop...only seat it lightly. Otherwise you'll cause damage to the seat. If you can get it to peak as above, find the peak point again and adjust the idle stop screw (not the air screw) to your requirements. Sometimes doesn't hurt to screw it in a further quarter turn from peak....too a degree, rich is better than lean... From memory if the peak revs are very low in the screw setting it a little lean, the opposite if at the outer end. You should not allow any more than 3 full turns out for adjustment...if it is coming in at or beyond this point then change the jet. The spring pressure on the screw starts to drop off about this point (Sudco recommendation) and the screw might fall out during operation...  If the bike feels down on power just off idle (at a steady throttle setting) - too lean; rough, wooly engine..black smoke/ too rich. The manual says that if the bike can't maintain a speed in the range of 12 to 25 MPH with a constant throttle, then the jet's too lean (small)... Only go 1 size at a time during changes. I run a 30 in my 38mm carb...280 main...might help you? Hopefully I haven't made you more confused... It is worth getting the Sudco Mikuni book...$12 US from what I see...I got one years ago for free...times have changed unfortunately... As an aside...my little Ducati 250 has a good system...it runs a Delorto SS1 with an air lever...much the same as an Amal TT carb. The air lever is always in the full open position for normal operation. This allows some compensation of the mixture for different days while on the run. These are a smooth-bore carb and not a good operating carb down low however... SR |
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Post by StewRoss on Jul 24, 2006 5:22:22 GMT -5
Check your messages as well.... SR  |
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Post by ccvogel on Jul 24, 2006 9:02:25 GMT -5
SR -
Again, your prompt and thoughtful posts are always appreciated.
Yes, the carb comes jetted for an SR500 with a K&N pod and an aftermarket exhaust.
Thanks very much for the info from the Mikuni tuning manual. [BTW, I recently downloaded a copy for free from the Mikuni website - didn't know what a bargain I was getting!].
RE: the air screw - after seeking the max idle speed, the setting is about 2 1/4 turns - still within the 2 1/2 turn limit that the manual specifies. I'm pretty sure the Pilot is a 35.
Ironically, I'm not having any problems except for the hard starting. Maybe I'll just have to live with it, because all else is fine - no problems upon acceleration in any gear. I was just trying to see if I could get the bike to start more readily.
How many kicks does it usually take you from cold, and do you use the "choke" in weather 75 - 80 deg F?
Thanks,
ccvogel
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Post by StewRoss on Jul 25, 2006 2:44:08 GMT -5
Hi,
Thanks for your kind words.
Really, the carbs end up being all a little different...like people...I have helped people do jetting on the same size carbs and often ended up with different settings, jets, slides etc. A good base setting is dependent on all of these things. Changing slides can also have a dramatic effect. Especially down low.
Lower slides richen it all up and higher cutaway slides lean it all out. Depending on how you go the setups can sometimes be a lot different. A different cutaway slide might help you out. However these things are not cheap and unless you are willing to do some cautious fileing or grinding it might be an expensive exercise. I did a 38 for a guy in Adelaide and he was perpared to do a lot of changing. We got that thing perfect, however, I neglected to get the final settings off him....oh well.
Choking (mixture enrichment) is a matter of practice and seeing what works. In hot weather you may not need any at all. Sometimes I have tried on some SR's kicking it over with a little throttle, kill switch on, and then leaving it alone and kicking through. Perhaps try these sorts of things. You'll eventually work out a system for yourself.
Try going to a 30 PJ and seeing what difference it makes...I'll be going through all this in a while with a Kei Hin CRS38....I've not played with one of these before......hmmm...
Have fun.
SR
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Post by ccvogel on Jul 25, 2006 8:35:34 GMT -5
SR -
I hadn't thought of part throttle; I'll try that.
If that doesn't work, maybe I'll change the PJ. I have a 30 on hand.
Thanks again for your help,
ccvogel
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