Otatts

It was worth the effort after seeing the original o rings out ports cleaned up and bike back together with new regular filter And ready to fire up I’ll spare my neighbours a 10pm engine revving and wait till tomorrow to see if this is all in vain

Being that I’d half dismantled the bike to change the air filter it made the task seem a little less daunting pulled the carbs out of both bikes. Got the original carbs for the 750 and put the OEM needles, emulsion tubes back in with the 112.5 mains decided to change the o rings and things went south quick as it does with this bike. Phillips head screws were seized in there and couldn’t get in there with an impact driver so the airbox had to come out....which meant the alternator had to come out which meant taking the sprocket cover off cracked most of them but had to drill a couple out that were already buggered from someone having a go at some point in its history

Ok so I managed to build up enough enthusiasm to face this thing again. So it’s time for an update i found the old air filter so decided to see what that would do. Ran a bit better as in it would get through the flat spot at 5-6000rpm but it’s still very much there. popped down to the suzuki dealer and got some stock size 117.5 mainjets and a set of o rings for the carb rubbers on the head. Got home and my new air filter had turned up. i decided to cancel out the original carbs from this bike having any vacuum leaks (though worn slides or worn throttle shafts) by installing the dynojet 1100 kit I’d been using in my 7/12 for the last two years and taking it for a run in the 7/12 bike ran perfect apart from some popping on closed throttle from the Smaller 750 pilot jets.......so there’s nothing wrong with the carbs. Which leads me to the conclusion it must issue between the needle/main jet Combo

Thanks @Blubber mine already has that insert too but it’s still breathing too much hence making another restrictor to go inside that. i might do as @Jaydeesaid an just get a stock filter and start from there. i just want the bastard to run properly enough to get me to work. Don’t care about outright power.....got the other one for that

@icpreyI just bit the bullet and bought a set of RS38’s for my 7/12 for when I put the DOT head on it as I was certain one of the two sets of bst36cv’s I have here was busted but now it look like they were both fine all along and it’s filter that’s creating the lean mix and not a vacuum leak. fuck it I needed an excuse to get the RS38’s anyway......can always sell one set 36’s to help cover the cost when all this is said and done. anyways I hope this helps you solve your problem. lemme know if you want my carb setting for my 7/12. It runs absolutely fine

@icpreyi feel like I’m finally making head way here after chasing my tail for 12 months. I’m just pissed as my other bike was bang on first go running pods and this one has been a pain in the neck and it’s almost stock! also swapped my K6 1000 track bike for this thing and it was suppose to be my daily Ride while I worked on my 7/12.....worked out the other way around!! glad to hear I’m not the only one

Whipped this up while bubs was having her arvo nap. started it up and it still has a flat spot but if I bring the revs up gradual it makes it through the flat spot so that’s an improvement! bike also woke the baby up so I’m going to have to wait till later before making more adjustments

@JaydeeOk so I warmed the bike up this morning then stuffed a sock down between the battery and filter opening to cover half the hole and it seems to have got rid of the flat spot! next question would be what would be the best standard filter to use? Ones from suzuki are $65 AUD guess I could make up another restrictor to go inside the existing one......save me buying another filter after spending countless $$ on this thing so far

@dezza I put fine wire down all the holes last time they were out of the bike. No sign of any gunk. I’ve put the DJ 1100 kit in them now and will try them in my 7/12 to see if it’s these carbs. Just waiting on one plastic needle ring from suzuki as I lost one with all this faffing around if it still runs like shit then there must be still crap in them or they’re sucking air somewhere

@Gixer1460correct. The DJ 1100 kit had all those bits and worked straight off the bat for my 7/12 running pods. Even had it dynoed and the air/fuel mixture was pretty bang on. 750 DJ kit didn’t have emulsion tubes so I just got new standard suzuki 750j tubes....Wrong move maybe? Also set it up as stage 1 not stage 3 like my B12 although I did try all the MJ sizes (120-124-140) except the largest 144 because I thought there’s no way it could be pulling that much air......although I could be wrong. That was with the paper style airbox filter that was in the bike when I bought it so I replaced that with new high flow as the mechanic I took it too said it could be old and sucking bits into the motor (was never sure on that logic) can’t be 100% sure the needles I pulled out were OEM but the profile is very similar to the new OEM ones I bought from suzuki (apart from the massive wear groove up top)...e.g rapid taper at the bottom of the needle. Both DJ needles (1100 & 750) have the same profile.....square bottom almost no taper would have put a pic up of the OEM needles I bought but I can’t face taking those fackin’ carbs out again!! Done this about 20 times over the last year and it’s a pain in the arse everytime! Bike has OEM needles, emulsion tubes, pilot jets and Mikuni 117.5 MJ’s in it now so going to try choke the airbox by shoving some cardboard between the battery and airbox tomorrow so I don’t have to pull the entire bike apart again and see what happens

Thanks @Jaydeegood info. kept thinking as it has an airbox so it couldn’t be that free flowing!......could be wrong Restrictor o ring is already in......my next experiment was to put my hand over the opening as I got to the flat spot to see if it made a difference. It would at least tell me if it’s getting too much air thanks for the input . I‘ll let you know home it goes

@Wee Manyeah when I bought the dynojet kit originally it didn’t come with emulsion tubes so I got a set of OEM ones from suzuki. Now I have OEM needles, emulsion tubes, Pilot jets, float bowl gaskets and o rings. All new

Do you think maybe 117.5 main jet is too big for OEM needles?? stock is 112.5

This pic is to show the difference in needle profile between OEM and dynojet dynojet left. OEM right the OEM ones are the fucked old ones hence the massive shoulder up top....new ones are in the bike at the moment flat spot seems to be where the taper changes on either needle......that’s me guessing

@MadJackyes correct. sorry if this is confusing as I’ve been trying to find out what the issue is by a process of cancelling out. both carbs are bst36cv’s one with dynojet 1100 kit and one with OEM 750 dyno jet carbs worked ok (With smaller mainjets to suit the 750) then put OEM 750 needles, emulsion tubes sand mainjets in and the flat spot is at 1/4 turn

The ones in it only had one hole. (2mm) the slides in it Now have had the dynojet mod done to each hole (dill, tap and insert grub screws) grub screw holes are approx 2mm diameter....so 2 2mm holes Same problem for either slide

I put the carbs from my 7-12 (36bst with dynojet 1100 kit) and put 124 dynojet mains and it ran good (very small hesitation at 8K) thinking my 750 carbs must have wear in the throttle shafts I put all the OEM 750 internals (new) in the working carbs and I have the same problem again!! Gah!! im at a loss...

Cleaned them up and put a dynojet kit in them and had a flat spot at around 8K so big that the bike would nearly stop. have been chasing the issue ever since. now I’m back to suzuki needles etc but a short list of stuff done/changes chasing this issue: tank cleaned, rust treated and sealed, new fuel tap (OEM), new fuel lines, fuel filters installed, needles and jets as mentioned. Swapped coils and leads from other bike, swapped CDI, swapped complete engine (original one had a knock in it) changed header from 4-2-1 to 4-1 (Made the flat spot at 8K wider but shallower) tried every jet size in the dynojet kit (120, 124, 140 & 144) and top,middle,bottom needle positions all it did was change the size and position of the hole but never get rid of it. went back to OEM and the flat spot is at 1/4 turn now

Bike barely ran when I got it but I thought it wouldn’t take much to fix it (how wrong I was!!) carbs were an absolute mess when I got it needles were a ‘touch’ worn

Hey guys. I’m appealing to the brains trust here. I’ve been battling my second bike for over a year now (between kid, work etc) trying time get it to run right. its a more or less bog stock ‘restored’ 1988 750j. Running a DNA high flow filter in airbox and 4 into 1 headers into an unknown can. starts up and idles fine but when I rev it it cuts out and dies at 1/4 - 1/3 turn. If bring it up slowly it gets to about 5Krpm and quits. If I pull the choke on it gets through the hole and goes off it’s head once through it currently has New stock suzuki 750 needles, new suzuki emulsion tubes, Mikuni 117.5 main jets, new pilot jets. I’ ve tried 122.5, 125, 130 mainjets and top, middle and bottom clip positions for the needle for each mainjet size. Each time it just moves the hole around a bit but doesn’t get rid of it carbs have been ultrasonically cleaned and balanced and new rubbers in the float bowls (gaskets and o rings)

Also something else I’d noticed while messing about with multiple carbs trying to solve a vacuum leak is that the carb caps are different heights on the slingshot 750 36bst (left) and mk1 bandit12 36bst’s (right). 25mm for the 750 and 30mm for the bandit. I noticed a couple guys using bandit carbs for the DOT/B12 in 750 frame builds with super tight fits so this might help get a few more mm clearance

Hopefully this is what you meant @Dezza still learning my way around the site. Wish I had of found this thread earlier. Great work guys

For anyone wondering about height differences between RS and CV these are some 38mm back to back. Measures about a 7-10mm difference. (He put a tape measure up to them but was kinda hard to make out in the pics)

That gives me hope @clivegto

Thanks @Dezzai did originally see they were mounted high between 3&4 and I think that’s why I thought they wouldn’t fit but was later told the cables actuator could be moved! i have a mate who has RS and CV’s and he’s going to measure from the Venturi to the carb cap top to see if/how much difference there is. It’s a tight fit already from what I’ve seen on here thanks to the other members ill start a project thread as I’ve been hijacking other people’s threads and I should just pull me finger out and do it