Runs with choke
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Hi guys, just rebuild my engine on a dtr I’ve just bought, did all gearbox bearings, crank bearings, con rod, all seals etc etc, bike sounds lovely.
But it only idles good on choke, soon as you put the choke down it still idles fine then you give it some revs and it hangs for around 5 seconds then dies down, almost like a lean / air leak, I’ve checked all the boots and they are tight with jubliee clips and it’s got brand new crank seals so wouldn’t think it’s that, on choke though you can rev it and dies down straight away.
Engine is a electric start one with a TM28ss flat slide carb
Pilot jet 22.5
Main jet 210
Needle clip middle
Carb doesn’t leakModifications to engine
1mm oversize piston
5mm reed valve spacer
Dep exhaust
Boyseen dual stage reeds with rev plate (so no metal reed fins)Any help would be amazing, thank you!
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Best thing to do would be a leak test sealing up the intake and exhaust, and pressurize it slightly. I usually 'cheat' by removing the carb, and putting in a plug with a tire valve in the intake, and feed it with some pressurized air (not to much pressure, or seals will blow out). Make sure piston is at TDC, or at least high enough to close the transfers. There will be some slight leak through the exhaust, but disregarding that, it should let you verify that the intake side and crank case is sealing. Listen for leaks at crank case sealing surface, flywheel side, and through the gearbox oil filling hole. You can also spray some soap water on the external sealing surfaces and watch for bubbles. A compressor with a variable pressure regulator is ideal, just adjust the pressure regulator to a really low value.
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Thank you! I will try that.
I’m also going to take the carb off and give that a good clean and maybe bring pilot jet up.I was just wondering does anyone have a Haynes manual or know the correct jetting for my engine it starts with E117E
It’s an electric start engine that’s in my dtr 1989
Little bit of research and it’s a 2004+ engine?
So just looking for the jetting first
Thank you again -
22.5 is right for the 210 main and year. Please don’t change the pilot jet, fix the problem
…Did it idle properly before the build? You have an air leak somewhere for sure. I usually spray brake/clutch cleaner around the rubber inlet while the engine is running…
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I know it’s correct for the year mate but remember I got Boyseen dual stage reeds, Reed spacer, dep pipe and forgot to mention I got snorkel removed as didn’t come with one with the bike, I’ll check tomorrow with spray in some areas around carb etc to see if it revs higher
Thanks -
so I bought the bike non running, mate got brand new top end for it, was running but same problem revs hanging, then when went to sell it wouldn’t start, the video I saw from the bike engine didn’t sound to healthy, so thought I’d take it all apart when I got into it the main bearing race was all broken so that’s why it sounded notchy, lucky I did as that could of ended bad if it seized. So rebuilt the whole engine, it sounds lovely now, the issue for not starting when I got it from him was faulty coil pack. I’ll try the spray tomorrow and report back thanks @SpookDog
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You’ve had the carb apart though? Cause you know the jet sizes? When I got my bike it had 1988 26mm jet sizes (180 main 20 pilot) fitted into a late 90s~2000 carb that used totally different 240 main.25 pilot. Just because the previous owner thought it was right, and I never knew better
…I went through every combination of jet years!
Thing is it’s not the year of the engine that matter, it’s the year of the carb. I blew head gaskets every 700miles for two years because I had too small a pilot jet, then a proper jet that was partially blocked with hard varnish/deposit. I wouldn’t of believed a pilot could cause such mayhem if I hadn’t lived it myself!!…
There are a couple ‘tell-tales’ that help you year your carb, I’ll look in the Haynes when I get home later on and post them…
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What I’m saying is they made 2 or 3 different Mikuni flatslide carbs, each with its own jetting. Mine is 240 main .25 pilot. Put a 210 & .225 in and it doesn’t like it!
You might have a later carb that a previous owner put earlier jets into… -
Whereabouts? I’ve got a slightly enlarged.25 & a 250 main you could try. If you do have the later carb the .25 airscrew is supposed to be 1 & 1/4 turns out. I’d try your setup at 1/2 to 3/4 turns…
I bounce between blandford and Poole…
PS I got a good copy jet at sportax racing. Couldn’t find a genuine in the UK
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Update:
Took the carb apart again, checked float height 16mm
Everything is perfect emulsion tube is missing an o ring, all the kits I see don’t come with one, but on my other dtr carb it has one. Where is best to get a rebuild kit that actually is decent rather than the Chinese cheap stuff? My needle is also bent, what needle code has everyone got?
Thank you,After that if nothing has changed then the left hand side seal has gone already I’m taking it even only being just fitted maybe the cheaper seals don’t last at all
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Little update: changed pilot jet from 22.5 all the way to 27.5 and no difference in running without choke, air screw not doing anything, put the needle to the richest possible still nothing, so it’s got to be an air leak only place now is the left hand side crank seal, I’ve replaced them all but they was only eBay ones so could be that, so gone with viton high quality one now.
What is the float height guys for the TM28ss? It’s at 16mm at the moment
Thank you -
If it’s your first time fitting them you may of fuxed up the inner spring or not seated them level. I’ve done it myself, more than once. You don’t have to split the cases to replace them…
I need to reread your thread to see what carb you have fitted. My memory is not wot it used to be … -
2004 onwards:
1DO I.D. mark
210 main
17.5 pilot
5J40 needle 2nd clip from Top
Q2M (938) emulsion tube
2.8 throttle slide cutaway
15.5 ~ 16.5 float heightYou may have an earlier carb though. Check the marks your needle & tube have on them…
The earlier one is:
I.D. 3MB00210 main
22.5 pilot
5J25 needle 4th groove from Top
Q-2 tube
2.5 throttle slide cutawayTry and suss out what carb you have by the slide cutaway. It’s stamped on it somewhere…
I may have a needle you can borrow to try swapping out. Let me know the markings on yours & slide…
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Thanks @SpookDog
My needle is NJ25
I’ve copied all them settings for my carb and still the same runs good with choke but soon as you turn it off it revs high then dies so definitely a lean state.I’ve ordered a viton crank seal now as I bet it’s that. Being cheap quality this one must of some how broke in the process of install.
As the air screw doesn’t change anything so got to be an airleak there as no where else it could be, as all the other gaskets, are
OEM from fowlers headgasket
And the rest of the gaskets are Vertex so decent
I just ordered a seal kit from eBay for £20 for the lot so that probably explains why the crank seal has gone already lol. These nitrile ones are not strong and no good with fuel I’ve heard.Other seal is arriving Tuesday/ Wednesday so I’ll update you then.
All the best everyone and thank you
