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Mikuni BS34 carb woes
Moderators: KeithZ1R, chrisu, paul doran, Taffus
Do all four pipes get hot when you run her on choke?,good way to test how hot pipes are running is with infra red thermometer or spray water on each pipe and see how quick it evaps.if all get hot on choke got to be issue with pilots,mains etc.
PAULJAC47,,,,,"She may not look like much, but she's got it where it counts, kid."
-Han Solo
You can't polish a turd, but you can roll it in glitter
Salad is what real food eats.
Anon
PUM 673
-Han Solo
You can't polish a turd, but you can roll it in glitter
Salad is what real food eats.
Anon
PUM 673
PAULJAC47 wrote:Do all four pipes get hot when you run her on choke?,good way to test how hot pipes are running is with infra red thermometer or spray water on each pipe and see how quick it evaps.if all get hot on choke got to be issue with pilots,mains etc.
No, 3 & 4 get hand hot quick, 2 gets warm after a while and 1 is cold, after 5 mins 1 will show just a little warmth, I run it on full choke then back to half.
Suggests poss another problem Graham as choke by passes the other jets,check fuel levels in bowls with manometer method first,get some clear pipe and screw into drain plug at bottom of carbs with plastic coupler,i get mine from local aqautics and strap to side of the carb,this will show level of fuel in each carb all should be couple of mill below bowl joint.
PAULJAC47,,,,,"She may not look like much, but she's got it where it counts, kid."
-Han Solo
You can't polish a turd, but you can roll it in glitter
Salad is what real food eats.
Anon
PUM 673
-Han Solo
You can't polish a turd, but you can roll it in glitter
Salad is what real food eats.
Anon
PUM 673
Manometer check will tell if you have stuck float or not enough fuel/level in carb, a check to see if its fuel releated.... on the choke side one of things i found was to gently blow down the air breather vent pipes,both should be just under the back of the tank,i had a set of these carbs that would not start on choke by blowing down the vent pipe it would start ok which led me to check out all the choke circuits..also a good check to see combustion is to use a Gunson colourtune,you can see whats happening in the cylinder straight away.
PAULJAC47,,,,,"She may not look like much, but she's got it where it counts, kid."
-Han Solo
You can't polish a turd, but you can roll it in glitter
Salad is what real food eats.
Anon
PUM 673
-Han Solo
You can't polish a turd, but you can roll it in glitter
Salad is what real food eats.
Anon
PUM 673
-
needaz1100r
- Custard Cream
- Posts: 601
- Joined: 11th Sep 2012
- Location: Reading
Suggested before, but have you actually removed the float valve seat. It's a 10mm (I think) brass "bolt". There is a filter on top of it.
If that gets almost blocked, you can still get fuel through, so when you check levels etc with the engine not running all seems fine, but fuel may not get in as fast as the engine uses it.
Try running the bike and spray WD40 into the carb, if it picks up when you do, you know it's a fuel issue.
If that gets almost blocked, you can still get fuel through, so when you check levels etc with the engine not running all seems fine, but fuel may not get in as fast as the engine uses it.
Try running the bike and spray WD40 into the carb, if it picks up when you do, you know it's a fuel issue.
Cheers,
Mark.
Mark.
Yes there all out Mark.
The carbs are now at my localish Motorcycle dealer as they have an ultrasonic carb cleaner that's big enough to take a bank of 4, and they will be rebuilding and checking them out
They did say if the carbs are really blocked it still wouldn`t get enough petrol on choke as it still sucks it up from the bottom.
Waiting on an old mate to lend me his compression tester.
Rocker cover gasket and air box rubbers ordered from Z power.
So now to be patient
The carbs are now at my localish Motorcycle dealer as they have an ultrasonic carb cleaner that's big enough to take a bank of 4, and they will be rebuilding and checking them out
They did say if the carbs are really blocked it still wouldn`t get enough petrol on choke as it still sucks it up from the bottom.
Waiting on an old mate to lend me his compression tester.
Rocker cover gasket and air box rubbers ordered from Z power.
So now to be patient
I am picking up the carbs tomorrow, I have looked in my Clymer manual about jet sizes, it seems the US K spec is different to the European J model.
K model main jet is 122.5R
jet needle is 5FL51
needle jet is Y1
European J Model main jet is 127.5R
jet needle 5FLZ50-3
needle jet Y6
what I would like to know is are the US jets bigger or smaller than the European J model, and if I do find an elusive Alfa what jets would be ideal for it with a standard air box.
One problem I do have is the number 3`s pilot jet is refusing to come out
Graham
K model main jet is 122.5R
jet needle is 5FL51
needle jet is Y1
European J Model main jet is 127.5R
jet needle 5FLZ50-3
needle jet Y6
what I would like to know is are the US jets bigger or smaller than the European J model, and if I do find an elusive Alfa what jets would be ideal for it with a standard air box.
One problem I do have is the number 3`s pilot jet is refusing to come out
Graham
1981 KZ1000 K1 LTD
Farm Boy with an O Level in Metalwork and not much else.
Everything in Sussex is a She, Except Tom Cat and She`s a He.
Farm Boy with an O Level in Metalwork and not much else.
Everything in Sussex is a She, Except Tom Cat and She`s a He.
Given the numbers you have posted above and the sizes of jets in the factory book; the US carbs for youre model are weaker across the range than the Euro J model carbs for what is essentially the same engine albeit a bit more peppy in the Euro J
Looks like the US versions are less adjustable too.
To fit the Alfa with standard airbox you may need to go one main jet size and possibly a pilot jet size up also.
However; this could leave you with a massive flat spot throughout the mid range.
I say this because the pilot air jets are massive and the jet needle looks like it only has one position!!!
Changing all the jets may be prohibitively expensive so Euro J model carbs might have been a better choice.
If you / they cant get that pilot jet out it may be a waste of time but i think 3 was running OK before?
1 and 2 were the issue so may still get away with it.
3 May loosen in the ultra sonic clean you never know.
AL
Looks like the US versions are less adjustable too.
To fit the Alfa with standard airbox you may need to go one main jet size and possibly a pilot jet size up also.
However; this could leave you with a massive flat spot throughout the mid range.
I say this because the pilot air jets are massive and the jet needle looks like it only has one position!!!
Changing all the jets may be prohibitively expensive so Euro J model carbs might have been a better choice.
If you / they cant get that pilot jet out it may be a waste of time but i think 3 was running OK before?
1 and 2 were the issue so may still get away with it.
3 May loosen in the ultra sonic clean you never know.
AL
1981 J1
Got the carbs back today, it was raining so only a couple of Moleing jobs, so I had an afternoon on it, fitted the carbs and she started up straight away and run fine, they couldn't get the number 3 pilot jet out so I`ll be looking for another body or J carbs complete in the near future
1981 KZ1000 K1 LTD
Farm Boy with an O Level in Metalwork and not much else.
Everything in Sussex is a She, Except Tom Cat and She`s a He.
Farm Boy with an O Level in Metalwork and not much else.
Everything in Sussex is a She, Except Tom Cat and She`s a He.
well its been a long haul, work and family have hindered my progress 
but today I had all four cylinders running nicely, my last battle was with the carb to engine rubbers, found number 3 was leaking so I brought four new ones, put them on and number 3 still wouldn`t run right, sprayed carb cleaner around all the rubbers and it wouldn`t pick up, sprayed it into the back of the carb and it picked !!, off with the carbs again, I`m getting very good at this now and stripped down number 3 to find nothing wrong, looked at the new carb to engine rubber and found a small blemish in the rubber, squeezed it and it showed a split right at the bottom, so got another sent out and all is fine, now for an MOT 
A big thanks to everyone that helped in answering my questions
but today I had all four cylinders running nicely, my last battle was with the carb to engine rubbers, found number 3 was leaking so I brought four new ones, put them on and number 3 still wouldn`t run right, sprayed carb cleaner around all the rubbers and it wouldn`t pick up, sprayed it into the back of the carb and it picked !!, off with the carbs again, I`m getting very good at this now and stripped down number 3 to find nothing wrong, looked at the new carb to engine rubber and found a small blemish in the rubber, squeezed it and it showed a split right at the bottom, so got another sent out and all is fine, now for an MOT
A big thanks to everyone that helped in answering my questions
1981 KZ1000 K1 LTD
Farm Boy with an O Level in Metalwork and not much else.
Everything in Sussex is a She, Except Tom Cat and She`s a He.
Farm Boy with an O Level in Metalwork and not much else.
Everything in Sussex is a She, Except Tom Cat and She`s a He.
.... and wheres Jimmock, he loves a happy ending 
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