nikos1400 Posted November 13, 2015 Share Posted November 13, 2015 To keep it short, my bike won't start after (apparently) going by the book when installing stage 3 Dynojet kit in my 38 cv Mikunis. I checked the plugs and they look like they might be fouled, could I give them a clean to save them?Anyway, the bike is a 1990 gsxr 750, with the bst38 mikunis. Stock headers, made link pipe and free flow end can. Dyna coils and k&n dual pod filters. I had the bike back from a mechanic who put some "K" 140 main jets in. Had the bike running....ok (could be a lot better), but he forgot the fuel tap filter that goes in the tank... Result was clogged fuel tap that barely got me home on prime after about 50-60klms.So I got the carbs 100% clean, had new o-rings in already. Got my fuel tap modified for on/off and a new filter. I decided to take a good look at the stage 3 Dynojet sheet, and do what it says myself. I left the same "140" main jets, and plugged the main air jets, which were not until then. I plugged them with zero jets and not the DJ "plugs".So basically I had the DJ stage 3 kit in, EXCEPT the float bowl plugs (to deactivate the powerjet). Also the K140 instead of the DJ 160 main jet.The bike started very easily cold, idled perfectly, and throttle response was like I've never seen !! The problem was #1 and 2 carbs were leaking and I think idle was getting rough after warming.Replaced #1 and #2 carb float bowls with the large cap to replace main jet, with some others I had extra. Result was not so smooth idle but still ok. Probably better than when I got it back from the mechanic.After some more research I read the article here about the powerjet and how it doesn't work without the airbox. So I plugged the float bowls which were open without any jets (!) and installed the DJ155 mains instead of the 160s because I don't have them any more...After that, it won't start!! Probably fouled the spark plugs in the process...Now what? Could it be "overfueled"? I check float height each time I put them back together, fuel is flowing from the tap. Floats are floating.I gave it another try, I wiped and blew the spark plugs and turned the pilot screws from dynojet's 2,5 turns out back to 2 turns. I had a little "gurgle" but no start....Some of my pics for reference: Quote Link to comment
Oilyspanner Posted November 13, 2015 Share Posted November 13, 2015 I can think of a couple of things Nikos - with dynojet kits you have to use their main jets they are different to Mikuni or Keihin jets and the jet needle will be sized for them, I'm guessing the 'k' jets are Keihin ?. As you have said the power jet system is only to be used with the airbox fitted , hence the bungs in the kit.Probably best to get new plugs, some more dynojet main jets. You are definitely running rich by the sound of it - too rich starts off better and gets worse with heat and the reverse for lean conditions. Are your float heights definitely set right, they make a big difference at the top and bottom end of revs - if they're a couple mm out the bike will run BAD ! Quote Link to comment
Jaydee Posted November 13, 2015 Share Posted November 13, 2015 Have a look at the chart and cross reference the keihin jets you have with their dynojet equivalent to see if you've gone too big in size. As said the numbers are different sizes between dynojet, keihin and mikuni. 2 Quote Link to comment
Scara Posted November 13, 2015 Share Posted November 13, 2015 My guess is the bike is flooding from the get go so : I'm going to ask a couple of questions for the OP to answer.WHAT are the correct OEM Size Main Jets that should be in the bike according to the workshop manual ?WHAT was the size of the Main Jets you removed before you started this exercise in fitting the Dynojet kit ?WHAT were the three DJ Main jet sizes you were provided in the kit for your bike ?HAVE you checked and reset your float levels at any time ? If so, what is the float height for each of the carburetors ?THE process to follow for all CV carb set ups which is pretty much fool proof: Check out another page here at OSS on BST40 Mikuni's http://old-skool-suzuki.proboards.com/thread/1239/mikuni-40mm-carbs-bst-bible To properly tune, you MUST:1. Have selected the BEST main jet for full throttle power (not just a "good" main jet - we mean "the BEST main jet" for power at high rpm). That eliminates the common severe tweaking of the midrange and lower tuning ranges to compensate for a "wrong" main jet.2. Then - select the BEST needle height / clip position for power at FULL THROTTLE / MIDRANGE after selecting the BEST main jet - That almost eliminates weird problems at cruise caused by tweaked needle heights that were required because the main jet wasn't correct.......3. Then, adjust the BEST Float Height for BEST FULL THROTTLE / LOW rpm You should be able to apply FULL THROTTLE at LOW RPM in TOP gear without ANY misfire of bogging or stumble.......If you follow that order, you will have: 1. Best topend. 2. Best midrange. 3. Best low rpm power.Then - all you have left is dialing in the pilot circuit - i.e. mixture screw and pilot jet size - That's IT -Don't tweak needle heights and throw away full throttle midrange to try to fix a cruise issue!!! (Unless you want to!)If you reach an impasse in steps 1,2 and 3 in the FULL THROTTLE tuning, STOP!!!!! and call TECH SUPPORT!!!415 491-5920 and 800 869-0497, ask for TECH SUPPORT -Cheers!Marc FROM FACTORY PRO WEBSITE DIRECT. Look forward to your response to my questions Quote Link to comment
Captain Chaos Posted November 13, 2015 Share Posted November 13, 2015 first of all make sure the float needles are not leaking.I have an original Suzuki GSX-R750L service manual at home, can post any specs you need this evening. Quote Link to comment
Captain Chaos Posted November 13, 2015 Share Posted November 13, 2015 and Suzukis are famous for eating spark plugs when trying to start with a battery which is not 100%. Be sure to charge it properly before starting, and with new spark plugs if possible. Quote Link to comment
nikos1400 Posted November 13, 2015 Author Share Posted November 13, 2015 (edited) Thanks for the quick replies guys My guess is the bike is flooding from the get go so : I'm going to ask a couple of questions for the OP to answer.1) WHAT are the correct OEM Size Main Jets that should be in the bike according to the workshop manual ?2) WHAT was the size of the Main Jets you removed before you started this exercise in fitting the Dynojet kit ?3) WHAT were the three DJ Main jet sizes you were provided in the kit for your bike ?4) HAVE you checked and reset your float levels at any time ? If so, what is the float height for each of the carburetors ?THE process to follow for all CV carb set ups which is pretty much fool proof: Check out another page here at OSS on BST40 Mikuni's http://old-skool-suzuki.proboards.com/thread/1239/mikuni-40mm-carbs-bst-bible To properly tune, you MUST:1. Have selected the BEST main jet for full throttle power (not just a "good" main jet - we mean "the BEST main jet" for power at high rpm). That eliminates the common severe tweaking of the midrange and lower tuning ranges to compensate for a "wrong" main jet.2. Then - select the BEST needle height / clip position for power at FULL THROTTLE / MIDRANGE after selecting the BEST main jet - That almost eliminates weird problems at cruise caused by tweaked needle heights that were required because the main jet wasn't correct.......3. Then, adjust the BEST Float Height for BEST FULL THROTTLE / LOW rpm You should be able to apply FULL THROTTLE at LOW RPM in TOP gear without ANY misfire of bogging or stumble.......If you follow that order, you will have: 1. Best topend. 2. Best midrange. 3. Best low rpm power.Then - all you have left is dialing in the pilot circuit - i.e. mixture screw and pilot jet size - That's IT -Don't tweak needle heights and throw away full throttle midrange to try to fix a cruise issue!!! (Unless you want to!)If you reach an impasse in steps 1,2 and 3 in the FULL THROTTLE tuning, STOP!!!!! and call TECH SUPPORT!!!415 491-5920 and 800 869-0497, ask for TECH SUPPORT -Cheers!Marc FROM FACTORY PRO WEBSITE DIRECT. Look forward to your response to my questions 1) Assuming the only differences between country codes for the carbs is the diff spec jets inside, I should be using the US specs on my 18D0 carbs (uk, fr, nor, belg, canada, spain) to install the Dynojet stage 3 kit ("for use in US models only", DJ 3135.004). So stock jets with stock airbox would be 127,5 main, 37,5 pilot jet. US models have the powerjet plugged with zero jets (plugs) in the float bowls, am I correct here? What I mean is that is what DJ is assuming? The carbs actually had the uk spec 117,5, 35 and 6ZD7 uk spec, but that was with the airbox and all this messing about.2) The mechanic had some "K"#140 mains installed (DJ emulsion tubes), pilot jets are/were 37,5. Float bowls without any jets in powerjet circuit, meaning free flowing (!). DJ needles on groove #2.3) The DJ160 mains DJ says to use with the stage 3 and free flow end can, are lost...I have the DJ155 mains left which I put in now that it won't start, for stock end can. I have some DJ 120 and 124 from the stage 1 part of the kit (was the stage 1 & 3 box).4) I checked the float height several times pretty much each time I put the carbs back together, with the cut-credit-card-template method. They might be 1mm off between them. I'd say they look pretty good. Now that you mention, what is a good way to adjust the tang without damaging it? I had to adjust one a little bit.first of all make sure the float needles are not leaking.I have an original Suzuki GSX-R750L service manual at home, can post any specs you need this evening.They were changed out when I put in some float valve kits and all o-rings. They look nice and appear to be working good. I know you can't tell from a pic of course Edited November 13, 2015 by nikos1400 Quote Link to comment
nikos1400 Posted November 13, 2015 Author Share Posted November 13, 2015 Would it be THAT hard to start with the DJ stage 3 installed ??What I did was half choke and no throttle. Nothing, then I tried a little bit of throttle, choke off....Nothing.One thing I remembered, last couple times, I did not disconnect the PITA throttle cable, and just emptied the float bowls, and turned the carbs upside down on the frame of the bike. Then took the float bowls off etc..Would that spill fuel inside the carbs somewhere it shouldn't ??? Can't think of something else. I'll be ordering some extra spark plugs and get the battery charged or a new one... Quote Link to comment
Captain Chaos Posted November 13, 2015 Share Posted November 13, 2015 (edited) as far as I remember the US-spec 750L has 36mm carbs.*edit* california-spec has 36mm carbs. But still the US-spec ones have completely different jetting. Edited November 13, 2015 by captain chaos Quote Link to comment
Captain Chaos Posted November 13, 2015 Share Posted November 13, 2015 Would that spill fuel inside the carbs somewhere it shouldn't ??? No. Quote Link to comment
nikos1400 Posted November 13, 2015 Author Share Posted November 13, 2015 capt, my haynes manual says US (except california)mains 127,5 - pilot jets 37,5 - main air jets 1 and 4 0.9mm, 2 and 3 1.2mmuk saysmains 117,5 - pilot jets 32,5 - main air jets 0mm (meaning plugged)both say needle jets O-8US (except california) jet needle 5ZDZ3UK jet needle 6ZD7-3It doesn't say anything about the Powerjet circuit though, which I'm not happy about... Quote Link to comment
Fula28 Posted November 13, 2015 Share Posted November 13, 2015 Fresh plugs, needed first , will help no end + full battery , however power jets are not enabled on these! Best 38's you can only get. Them from factory pro super sport kit. And even then they Only work with stock airbox and operate at 3/4-full throttle. Not worth it really it. Quote Link to comment
Captain Chaos Posted November 13, 2015 Share Posted November 13, 2015 It doesn't say anything about the Powerjet circuit though, which I'm not happy about...the powerjet circuit came blocked from the factory (jet size 0) on all markets. Quote Link to comment
Captain Chaos Posted November 13, 2015 Share Posted November 13, 2015 One more thing. In each plastic brown float holder there should be a jet pressed in, for the choke circuit. These tend to fall out and without them they are a right bastard to start. 1 Quote Link to comment
suzook12 Posted November 14, 2015 Share Posted November 14, 2015 capt, my haynes manual says US (except california)mains 127,5 - pilot jets 37,5 - main air jets 1 and 4 0.9mm, 2 and 3 1.2mmuk saysmains 117,5 - pilot jets 32,5 - main air jets 0mm (meaning plugged)both say needle jets O-8US (except california) jet needle 5ZDZ3UK jet needle 6ZD7-3It doesn't say anything about the Powerjet circuit though, which I'm not happy about...Strangely, I have never come across any GSX-R with 0 air jets, 7 or 11's. I do however think you are massively overjetted. My 750m with full stage 3 kit had dj145's fitted, and on 7's I use 140 Mikunis as a starting point. Having found some take 135's and the odd one requiring 145's.Stage 3 kits also seem to make bikes hyper sensitive to float heights.....Steve Quote Link to comment
nikos1400 Posted November 14, 2015 Author Share Posted November 14, 2015 (edited) Strangely, I have never come across any GSX-R with 0 air jets, 7 or 11's. I do however think you are massively overjetted. My 750m with full stage 3 kit had dj145's fitted, and on 7's I use 140 Mikunis as a starting point. Having found some take 135's and the odd one requiring 145's.Stage 3 kits also seem to make bikes hyper sensitive to float heights.....SteveThanks Steve,I guess I'm going to try and get it started to begin with, I've ordered some new spark plugs.The K140 mains (I guess Keihins?) correspond to DJ130. Dynojet states DJ160 for the stage 3 with end can, DJ155 w/ stock end can.But the mains supposedly don't affect idle and low rpm ??Anyway, it fired up easy with powerjet circuit 100% open and K140 mains, won't start with DJ instructed plugged powerjet and DJ160s... About the float heights.... I hope I'm doing it right.I help keep the whole plastic frame seated with fingers (as if the bowl cap was screwed on), measure float height with the credit card template for 14,6mm. Floats barely seated on the needle pin without pressing it down. I might be 1mm off at max. Is it too much? Haynes says +/- 1mm. Edited November 14, 2015 by nikos1400 Quote Link to comment
1168turbo Posted November 14, 2015 Share Posted November 14, 2015 carbs are a fuckin nightmare if you don't know what you are doing...I don't...that's why my slingy has sat for 4 years! 1 Quote Link to comment
nikos1400 Posted November 14, 2015 Author Share Posted November 14, 2015 carbs are a fuckin nightmare if you don't know what you are doing...I don't...that's why my slingy has sat for 4 years!You're right! But thank god for the internet and people who help other people!! Quote Link to comment
Rene EFE Posted November 15, 2015 Share Posted November 15, 2015 and Suzukis are famous for eating spark plugs when trying to start with a battery which is not 100%. Never a truer spoken.I personally have a big dislike for 38's and Dynojetkits, in that order. Put them together and you have my equivalent of a nightmare.What you're experiencing is exactly what we found on @Jelly's bike. I've thrown the towel in the ring and think we should change them for 36's.I had them on all oilcooler I've built and I can set them up blindfolded, they're the exact opposite of the 38's.I'm sorry that I can't help you to a solution to your problem, to me, the 38's are just not worth the effort; they suck. Quote Link to comment
Captain Chaos Posted November 15, 2015 Share Posted November 15, 2015 38's are easy to set up on an 1100 or 1200 engine, but difficult on a 750. Like Rene says the 36's are easy to set up on almost any engine. Quote Link to comment
nikos1400 Posted November 15, 2015 Author Share Posted November 15, 2015 I'm trying to get permssion from the wife to spend 900+ euro on some mikuni rs34s...Would they be easier? LOL Quote Link to comment
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