richyrich Posted March 10, 2016 Posted March 10, 2016 hi i had a dream my newly fitted 750L engine and its mikuni bst38 carbs worked ok with its ramair filters, in the gs550. It wasnt a dream it ran from cold and i even rode it once. Now it wont start.... Nikos1400 started a good thread in November about this and the conclusion was, the 38s' are a nightmare and new plugs and battery sorted him out. I cant be throwing new plugs in to watch them get fouled in short order. My HT is good and the battery should be good enough as it turns it over hard. Its interesting that the one time ive ridden it, i started it plugged into the shops bigass charger, so new battery is probly good advice but not the whole answer. which has got me thinking. So back to carburation. Its got 155 main jets in it, which should match the ramair socks as a starting point. It drives me crazy cos for a while it started and idled, quite high idle and its like the throttle cable was sticking, but it proved it worked and i got on with putting the rest of it together. The only thing ive changed since those long gone easy start days is stupid shit like wiring in tail lights and my deluxe wooden tank mount. So what gives... Its the fouled plugs from starting it and not riding, getting it up to temp to burn off the foul deposits, the shit. So its constantly flooding and the spark is not strong enough to ignite it. This is an interesting article......http://tonysleep.co.uk/info/great-gsxr400-carburettor-saga Hes basically saying the o rings keeping the fuel in the float bowl from the charge get imperceptably knackered and let loads of fuel through. Thus making the metering of the starting and main circuits kinda pointless, as it will be way too rich anyway whatever tune you do. So my plan is to pay a well known manchester carb o ring supplier, as recomended by robinsons foundry, a lot of money for a small amount of well formed, petrol resistant, rubber. then see if my spark is good ebnough to start it. What does the oss hive mind think of this plan and about the above article. Good day chaps Quote
wraith Posted March 10, 2016 Posted March 10, 2016 If it's the o rings that fit under the brass nedel jet holder you can get them from Robinson's for not to much, if these have gone you will see the fuel coming out the back of your carbs (or it did when mine went) I am using the 38mm on my 1127 and have got 144 main jets in and that spits flames out of the zorst on shout off and is running rich, so I would say 155 main may be a bit big for the 750 motor? What's your compression like? Are the plugs wet or oily, I take it the valves are at the right setting and not to tire? Is your spark a good strong blue ? Pilot jets, are they clear, if the bike has not been run for a time they may have some crud in their try setting them at 2.5 turns out. Just some starters Quote
boilerdude Posted March 11, 2016 Posted March 11, 2016 I'm no expert here but wouldnt 155 mains be entirely too big for a gs550? Quote
boilerdude Posted March 11, 2016 Posted March 11, 2016 shit sorry.. 750 engine... not just the carbs. whole gsxr 750 plant.... in a gs 550. gotcha. sorry. Quote
nikos1400 Posted May 16, 2016 Posted May 16, 2016 On 3/9/2016 at 8:58 PM, richyrich said: hi i had a dream my newly fitted 750L engine and its mikuni bst38 carbs worked ok with its ramair filters, in the gs550. It wasnt a dream it ran from cold and i even rode it once. Now it wont start.... Nikos1400 started a good thread in November about this and the conclusion was, the 38s' are a nightmare and new plugs and battery sorted him out. I cant be throwing new plugs in to watch them get fouled in short order. My HT is good and the battery should be good enough as it turns it over hard. Its interesting that the one time ive ridden it, i started it plugged into the shops bigass charger, so new battery is probly good advice but not the whole answer. which has got me thinking. So back to carburation. Its got 155 main jets in it, which should match the ramair socks as a starting point. It drives me crazy cos for a while it started and idled, quite high idle and its like the throttle cable was sticking, but it proved it worked and i got on with putting the rest of it together. The only thing ive changed since those long gone easy start days is stupid shit like wiring in tail lights and my deluxe wooden tank mount. So what gives... Its the fouled plugs from starting it and not riding, getting it up to temp to burn off the foul deposits, the shit. So its constantly flooding and the spark is not strong enough to ignite it. This is an interesting article......http://tonysleep.co.uk/info/great-gsxr400-carburettor-saga Hes basically saying the o rings keeping the fuel in the float bowl from the charge get imperceptably knackered and let loads of fuel through. Thus making the metering of the starting and main circuits kinda pointless, as it will be way too rich anyway whatever tune you do. So my plan is to pay a well known manchester carb o ring supplier, as recomended by robinsons foundry, a lot of money for a small amount of well formed, petrol resistant, rubber. then see if my spark is good ebnough to start it. What does the oss hive mind think of this plan and about the above article. Good day chaps Crap. I just searched for "fouled plugs" and my name comes up here...LOL! About my bike, I let it sit too long I guess, waiting for some 160 main DJs to arrive and shitty weather to go. About a month or more, I don't know. Life, kids, work etc... Anyway I put the 160s in today and started it up on that old battery I had charged back then, started up OK at first but it appears I fouled at least one plug. Ordered some new plugs again, that's another 35 euro, I'm going to charge the battery before I fire up again also but I'm honestly thinking of trading the 38s in for something else. ... Quote
Phill106 Posted May 17, 2016 Posted May 17, 2016 (edited) I'm no expert but it sounds like the the a/f is way off and flooding the engine. I'm not sure about the 750 carbs but the jets shouldn't be too much bigger than those. I wouldn't think that going from 155 to 160 jets will help. One thing I'd also check is oil contamination. A quick sniff will normally give you a good indication, if it reeks of fuel then you may have washed out the cylinders. Check compression to confirm this. Edited May 17, 2016 by Phill106 Quote
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