Oh, Come On! I Changed The Main Jet On My 250 And Now It WILL NOT START!!!

Aufgeblassen · 10-25-2021, 12:30 PM

WTF? I went from an 88 main jet to a 110 on my 2021 Tao Motor TBR7 "250". I know I have it together correctly (after a few tries). It cranks and cranks, but no start. Once it almost started, before battery ran too low to crank further.

Note: The head of the the new main jet screw is quite a bit larger than factory, but I don't see how that could be an issue as it is on float bowl side of carb.

Any ideas?

2LZ · 10-25-2021, 12:47 PM

Quote:

Originally Posted by Aufgeblassen

Note: The head of the the new main jet screw is quite a bit larger than factory,

Any ideas?

Sounds like a Mikuni jet put in a PZ???? Just guessing without pics

J4Fun · 10-25-2021, 01:01 PM

I assume WTF means What's The Fix? Maybe the float bowl wasn't quite filled yet when you were cranking? Just a thought

mototech77 · 10-25-2021, 01:01 PM

Are you getting a gasoline smell when cranking? If so, this may be a shot in the dark, but I’m thinking it’s possible the needle may be set too high. If so, it could be spraying fuel from the main jet before the throttle is opening.

If you aren’t smelling fuel, since you had the carb apart, don’t rule out the simple things or the possibility of something unexpected like the float valve needing readjustment if the float tab accidentally got tweaked.

TominMO · 10-25-2021, 01:22 PM

Kill switch in the Off position?

mototech77 · 10-25-2021, 01:26 PM

Quote:

Originally Posted by TominMO

Kill switch in the Off position?

Man, you aren’t kidding.

I have gone through troubleshooting all kinds of things and it would end up being something that simple. (petcock is off because I turned it off to remove the carburetor). Lol

Aufgeblassen · 10-25-2021, 04:29 PM

Quote:

Originally Posted by TominMO

Kill switch in the Off position?

In EITHER position it cranks!!! Seems like in only one it should.

TominMO · 10-25-2021, 05:26 PM

Quote:

Originally Posted by Aufgeblassen

In EITHER position it cranks!!! Seems like in only one it should.

No, it cranks in both. When I first started up my Lifan, it was in the Off position. Cranked but didn't fire until I flipped it to On.

How about the petcock? Is it on? Enough gas?

dirtbkr188 · 10-25-2021, 05:53 PM

I'm curious as to reason for going from a #88 to a #110 main jet in one shot...

There has to be other sizes in between 88 and 110 to try, usually one size bigger, at a time, and then see if the performance improves.

Aufgeblassen · 10-25-2021, 05:55 PM

Quote:

Originally Posted by TominMO

How about the petcock? Is it on? Enough gas?

Yes and yes.

Aufgeblassen · 10-25-2021, 05:56 PM

Quote:

Originally Posted by 2LZ

Sounds like a Mikuni jet put in a PZ???? Just guessing without pics

Does it matter??? 110 is 110 in either case.

FlyingBasset · 10-25-2021, 06:07 PM

Quote:

Originally Posted by Aufgeblassen

Does it matter??? 110 is 110 in either case.

Yes it does matter. Mikuni and Keihin jets are not sized the same.

https://www.blasterforum.com/attachm...son-jpg.13852/

By the way, your responses and comments on this forum often come off as very combative - especially to people trying to help you. I'm guessing it's a translation/ culture thing.

TominMO · 10-25-2021, 06:20 PM

It should start even with a too-large main jet, since the pilot jet would be the one involved at low RPMs. I wonder if the fuel or air mixture screw is turned all the way in. I'd suggest you go over everything again from square one, to make sure you didn't miss anything.

Aufgeblassen · 10-25-2021, 09:13 PM

Quote:

Originally Posted by TominMO

. I wonder if the fuel or air mixture screw is turned all the way in.

If it was, it never would have started from the get-go. It worked fine up to about 40 MPH, at which time I had to partial to fully put choke on, especially to accelerate, or else it would stumble.

And no, I did not touch the air/fuel mixture screw one iota.

China Rider 27 · 10-25-2021, 10:32 PM

I would verify you have spark. Verify you have gas to and in the carburetor. Then I would take that carburetor apart again and go over it with a fine tooth comb since it worked before it was disassembled. Verify the slide works properly on the bike with throttle cable. Verify the float and needle is not stuck. Float level is correct. You should be able to hear the float move back and forth when moving it off the bike. I have had carbs would not start the bike put back on after cleaning because the slide was not open enough to allow some air at start up (idle speed screw was not adjusted correctly). What kind of carburetor is it?

10-25-2021, 01:01 PM	#4
mototech77 Join Date: May 2021 Location: Central Florida Posts: 80	Are you getting a gasoline smell when cranking? If so, this may be a shot in the dark, but I’m thinking it’s possible the needle may be set too high. If so, it could be spraying fuel from the main jet before the throttle is opening. If you aren’t smelling fuel, since you had the carb apart, don’t rule out the simple things or the possibility of something unexpected like the float valve needing readjustment if the float tab accidentally got tweaked. __________________ 2021 Lifan Xpect EFI 2012 DF250rtc 1982 Yamaha Virago XV750 1982 Honda Twinstar CM200
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10-25-2021, 01:22 PM	#5
TominMO Join Date: Sep 2021 Location: De Soto, MO Posts: 2,042	Kill switch in the Off position? __________________ 2021 Lifan Xpect--sold 2022 Lifan KPX 1972 Honda CT90--The Carrot 1969 Honda CT90--The Tomahto Cheesy is the WDK (workplace drama king). Now retired. Nope, back in the saddle. Nope, finally retired. Climate: The Movie https://www.youtube.com/watch?v=A24fWmNA6lM How our government really works https://www.youtube.com/watch?v=QjadCd0VRBw Question all authority.....think for yourself
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10-25-2021, 06:20 PM	#13
TominMO Join Date: Sep 2021 Location: De Soto, MO Posts: 2,042	It should start even with a too-large main jet, since the pilot jet would be the one involved at low RPMs. I wonder if the fuel or air mixture screw is turned all the way in. I'd suggest you go over everything again from square one, to make sure you didn't miss anything. __________________ 2021 Lifan Xpect--sold 2022 Lifan KPX 1972 Honda CT90--The Carrot 1969 Honda CT90--The Tomahto Cheesy is the WDK (workplace drama king). Now retired. Nope, back in the saddle. Nope, finally retired. Climate: The Movie https://www.youtube.com/watch?v=A24fWmNA6lM How our government really works https://www.youtube.com/watch?v=QjadCd0VRBw Question all authority.....think for yourself Last edited by TominMO; 10-26-2021 at 11:38 AM.
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10-25-2021, 12:30 PM	#1
Aufgeblassen Join Date: Sep 2021 Posts: 85	Oh, Come On! I Changed The Main Jet On My 250 And Now It WILL NOT START!!! WTF? I went from an 88 main jet to a 110 on my 2021 Tao Motor TBR7 "250". I know I have it together correctly (after a few tries). It cranks and cranks, but no start. Once it almost started, before battery ran too low to crank further. Note: The head of the the new main jet screw is quite a bit larger than factory, but I don't see how that could be an issue as it is on float bowl side of carb. Any ideas?
	0

10-25-2021, 01:01 PM	#3
J4Fun Join Date: May 2021 Posts: 375	I assume WTF means What's The Fix? Maybe the float bowl wasn't quite filled yet when you were cranking? Just a thought
	0

10-25-2021, 05:53 PM	#9
dirtbkr188 Join Date: Aug 2009 Posts: 592	I'm curious as to reason for going from a #88 to a #110 main jet in one shot... There has to be other sizes in between 88 and 110 to try, usually one size bigger, at a time, and then see if the performance improves.
	0

10-25-2021, 10:32 PM	#15
China Rider 27 Join Date: Dec 2018 Location: PNW Posts: 985	I would verify you have spark. Verify you have gas to and in the carburetor. Then I would take that carburetor apart again and go over it with a fine tooth comb since it worked before it was disassembled. Verify the slide works properly on the bike with throttle cable. Verify the float and needle is not stuck. Float level is correct. You should be able to hear the float move back and forth when moving it off the bike. I have had carbs would not start the bike put back on after cleaning because the slide was not open enough to allow some air at start up (idle speed screw was not adjusted correctly). What kind of carburetor is it?
	1