Fueling problem 1200 Bandit. Carb expertise needed.

Gimlet

Gimlet

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Asking for a friend.. No, I really am. I haven't bought one but he has after an 11 year break from biking.
It's a 2005, the last of the carburettor models. It's a very clean bike, owned by the previous owner for years and came with a 12 month ticket and a full service, including apparently a complete carb overhaul.

It runs sweet as a nut on the power but today he was having trouble with tickover and when taxi-ing at walking pace for refueling etc. Sometimes it dies at tickover or stalls just off tickover when he touches the throttle. He's not mechanically minded and he's asked me what I think.

It sounds to me like there's a problem with the pilot jet fueling, or possible a vacuum leak somewhere - though the revs aren't hanging when he shuts the throttle at speed. He assures me (or the previous owner does) that the carbs had a full strip and rebuild last year.

I'll probably have to help him fix it but it's been years since I fettled anything with carbs so just looking for pointers on where to start or whether there were any known fueling issues with these bikes that should be investigated first.

Genuine enquiry for a mate. Any ideas appreciated.
 
SHarper said:
I think pilot jets too.
Standard carbs and airbox?
Did the carb overhaul involve a Dynojet kit?
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Derek said:
Gummed up pilot jets. With modern fuels it happens if the bike is unused for few weeks
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Unsure how long the bike's been stood. It will be weeks. Carbs and airbox are standard. As far as I know, no Dynojet.

Bearing in mind the bike is 20 years old, I think we should flush the tank as best we can and fit an in-line fuel filter. I don't know if it has one. I didn't think to look earlier but I can't remember seeing one. With rubber diaphragm CV carbs I guess he should stick to E5 fuel as well.

Just asking as some older Jap carbed bikes were notorious for irritating fuel niggles. I had a Yam XJ with the YICS system back in the day and that was a pig for carb balancing, vacuum leaks and hanging revs.

I will suggest a carb strip, tank flush, pilot replacement and a fuel filter. He'll probably want a quick and cheap fix which won't work and I don't want him to lose his enthusiasm so I'll volunteer to do it myself.
 
My XJ900F had wonderful fueling except for a flat spot at 4500rpm.
I blame the Motad 4-1 system I used to replace, after two years, the OEM 4-2 which was made from some kind of shiny cardboard I reckon.
 
Loz said:
My XJ900F had wonderful fueling except for a flat spot at 4500rpm.
I blame the Motad 4-1 system I used to replace, after two years, the OEM 4-2 which was made from some kind of shiny cardboard I reckon.
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Motad 4-1's fitted to my cbx550f2 and cbx750 as honda's zorst's liked to rot from the inside out!
 
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Gimlet said:
Unsure how long the bike's been stood. It will be weeks. Carbs and airbox are standard. As far as I know, no Dynojet.

Bearing in mind the bike is 20 years old, I think we should flush the tank as best we can and fit an in-line fuel filter. I don't know if it has one. I didn't think to look earlier but I can't remember seeing one. With rubber diaphragm CV carbs I guess he should stick to E5 fuel as well.

Just asking as some older Jap carbed bikes were notorious for irritating fuel niggles. I had a Yam XJ with the YICS system back in the day and that was a pig for carb balancing, vacuum leaks and hanging revs.

I will suggest a carb strip, tank flush, pilot replacement and a fuel filter. He'll probably want a quick and cheap fix which won't work and I don't want him to lose his enthusiasm so I'll volunteer to do it myself.
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Aye Jim yer a good mate, after the procedure, tell your mate to shut the fuel tap, running the carbs empty if he's gonna lay the bike up for any length of time.
 
BobTheBounder said:
Motad 4-1's fitted to my cbx550f2 and cbx750 as honda's zorst's liked to rot from the inside out!
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I had a Motad on my CB750Kz. It rotted at the collector where all the down pipes met (and all the crap gathered). It gave good performance but the metal was paper thin.
I had one on an XJ750 to replace the rotting stock 4:2 and it wasn't as good on that. It pushed all the power up top andleft it flat in the middle.
 
I hate carbs 😞.

@Derek is probably right.

Vacuum leak is easy to test for just spray brake/parts cleaner around the inlet manifold when it’s ticking over/running, see what, if anything, happens to the revs - hopefully nothing if there’s no air leak.
 
I did a carb rebuild on one of these about 8 weeks ago and concur with what Derek and WestCorkRoofer have said. Do the vacuum leak first as an initial test and then pull the carb set out. It is worth retaining the carb heaters but you can get rid of all that PAIR valve emissions pipework while you have the tank off. I am talking about the four pipes that loop over the top of the engine and breathe into the exhaust ports. I cut the pipes about 8mm up from the flange and then tapped them to either 5 or 6mm and loctited some short bolts in and reinstalled the blocked off flanges.
The carbs themselves are easy and some very careful setting up with a new jet kit and then a very careful carb sync should see you right.
Here is a pic of all the junk I removed plus the pair valve flange mod
75978824863__2EE3B5FF-FBCD-40AC-9907-459DCA5A1B88.webp
IMG_8717.webp
 
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