Author Topic: 750/4 carbs (Read 3110 times)

maystarbmw · « **on:** July 07, 2006, 02:17:17 PM »

sorry to be thick but i cant seem to figure out why every time i turn on the fuel tap, petrol is pouring out of the air filters. i have cleaned all the float needles, they all move smoothly, if i remove the float chamber covers and hold the floats up no fuel leaks, as soon as i put covers back on fuel comes out of filters and overflow, This is a project bike and has been off of the road for a while, but desperatly trying to get it on road this summer,

Bob Wessner · « **Reply #1 on:** July 07, 2006, 03:06:00 PM »

What are the float heights set at? What year/model and do you have a manual for the height specs? They may close when you do it manually as discribed, but they may be too high in the bowl (when the bowl is on) so the fuel overflows.

750goes · « **Reply #2 on:** July 07, 2006, 03:11:08 PM »

are there any needles in the carbies, the ones that the float presses on to stop fuel flow, if yes are they stuck?/??

maystarbmw · « **Reply #3 on:** July 08, 2006, 03:52:05 PM »

Yes the float needles are running smooth, i will try and figure out which model it is to check the float height,

750goes · « **Reply #4 on:** July 08, 2006, 04:24:43 PM »

if you cleaned the jets, I think you may have put the floats back in upside down (it's easy to do), this would definitely cause some problems, show us a few pictures with the bowls off may help a bit...

Bob Wessner · « **Reply #5 on:** July 08, 2006, 05:05:40 PM »

Quote

I think you may have put the floats back in upside down

Ooh, hadn't thought of that. That would definately do it also. You get an "A" for thinking outside the box.

Jonesy · « **Reply #6 on:** July 08, 2006, 06:45:25 PM »

Quote from: Bob Wessner on July 08, 2006, 05:05:40 PM

Ooh, hadn't thought of that. That would definately do it also. You get an "A" for thinking outside the box.

...Or outside the carb bowl...

750goes · « **Reply #7 on:** July 08, 2006, 06:54:43 PM »

I stripped and reassembled some carbs I bought from ebay last week

Had one full set - jetted mains 120 slows 40
carb #4 had the main jet sitting in the bowl - someone had overtightened the emulsion tube/jet - broke about 5mm off the carb body - chucked that away, and with the extra 4 separate carbs stripped (all pieces in a plastic tub) and cleaned another one to replace it.
The bits'n'pieces carbs had jets of 130 mains 40 idles.

I put the floats in upside down before I had a think about it - too much of a rush to get it done. then thought I should check, yeah I did them all upside down... would have been fun when I get round to synching, tuning them.

any more progress on the problem..

maystarbmw · « **Reply #8 on:** July 08, 2006, 07:20:16 PM »

How do i put up pictures, if i could put some up you technical people could figure out what im doing wrong and possibly identify my bike model as well, i think its an f2, because of the alloys and twin disks, but i dont know if UK spec is the same as US

cbjunkie · « **Reply #9 on:** July 08, 2006, 07:54:07 PM »

just post the serial numbers from the engine and frame - somebody will look it up for you

if you want to post pix hit the "additional options" button at the bottom left side under your text box when you are typing - a standard "browse" button comes up and you can add more if you want

it's finicky about the size - 125 kb, max, i think...

hope this helps...
junkie out.

maystarbmw · « **Reply #10 on:** July 08, 2006, 08:05:03 PM »

i hope this picture helps towards identifying my bike, as u can see i have butchered it a bit, each to there own taste i say

cbjunkie · « **Reply #11 on:** July 08, 2006, 08:12:08 PM »

like i said - post your frame and engine number - takes the guesswork out...

750goes · « **Reply #12 on:** July 09, 2006, 01:57:22 AM »

Looks like an F1 or F2 - black motor - but don't know much

grab the Vin & Engine Number - easy to sort out then - a few more photos if you can please, specially those carb bowls removed and the floats just sitting there..would be good to maybe solve your problem.

maystarbmw · « **Reply #13 on:** July 09, 2006, 07:59:27 AM »

fr no= CB750G1001439, eng no= B750GE1001210

maystarbmw · « **Reply #14 on:** July 09, 2006, 08:02:35 AM »

PICTURE

maystarbmw · « **Reply #15 on:** July 09, 2006, 08:06:24 AM »

ANOTHER PIC

maystarbmw · « **Reply #16 on:** July 09, 2006, 01:23:20 PM »

do the pics help anyone explain whats wrong

maystarbmw · « **Reply #17 on:** July 10, 2006, 01:31:15 PM »

fr no= CB750G1001439, eng no= B750GE1001210, ANY CLUES PLEASE ANYBODY

STLrocker · « **Reply #18 on:** July 10, 2006, 08:54:02 PM »

the bike looks like a 77 or 78 F. the carbs look like the type that came on that bike, but i remember them having rubber floats instead of the plastic ones you have. it may have changed somewhere during production.

at any rate to be sure of the carbs you have you can look at the number on the side of the carb body. it should be stamped into the body just above where the float bowl goes. for the later F models you should have either PD41B or PD42A.

if it's either of the numbers, your float height should be 14mm - 15mm.

if its something else, post the number.

couldnt find any info for your engine or frame numbers. dont ever remember seeing a G anywhere only F, E, and A, but it may be a UK thing.

Sam Green Racing · « **Reply #19 on:** July 10, 2006, 09:25:14 PM »

How about a fuller on pic instead of engine and back wheel

750goes · « **Reply #20 on:** July 11, 2006, 12:37:21 AM »

Cannot find that Frame and Engine Number

I could also not enhance the picture enough to see clearly the carb floats..

But behind the main jet it appears there is another hole - is this threaded at all ? I'm also not familiar with those carbs.., but it could possibly be for an idle or slow jet

not really much help there... sorry..

maystarbmw · « **Reply #21 on:** July 11, 2006, 03:43:54 AM »

The number on the carbs is = V321 BB25

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Author Topic: 750/4 carbs (Read 3110 times)

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