Carb problem, need help

[Dontron]

And the winner is ... valve clearances !!!

All the valves were tight, I adjusted them, now the bike starts and idles very nicely.  Thank you nhmaf and montmil !


BUT - now the bike is losing power at medium engine speeds. WTF???

Standing by to accept more suggestions!

Thanks again,

Don

[Barry]

A couple of possibilities :-

A flat spot at 3000 - 3500 RPM that clears at higher revs can be needle position is too low. Check factory position and maybe move up one click if needed.


Losing power at higher revs say at 60 mph is often torn diaphragms

[montmil]

A couple of possibilities... Losing power at higher revs say at 60 mph is often torn diaphragms

UhHuh. That be me sometime back. Hit 60mph and the stutters began. Couldn't see any damage to the diaphragms but with new Bing rubber, it runs to the ton. Buy Bing originals. Don't care what some folks may say about repop diaphragms; they're not the same.

Monte

[Dontron]

Well, I can use some more help!

To recap:

Bike started idling poorly, not making any power on the left cylinder.

I cleaned idle jet, no improvement. Cleaned entire carb, no improvement.

Checked valves - all were very tight, especially the left side exhaust. Adjusted them.

The bike started better and idled very well, but now started bogging down very badly at mid rpm’s.

Checked the points, they were very tight, adjusted them.

Checked timing, it was a couple of degrees advanced, adjusted it.

Bike still lost power badly at mid range rpm’s.

Raised the left needle one notch (to the highest position). Checked the right needle and found it was already in the highest position.

Slight improvement but bike still bogs down and loses power at mid-range rpm’s.

What now?  Time to rejet?  It has  #140 jets in it right now.

Thanks ... again.

Don

[Rob Valdez 79 R65]

Have you opened the top of the carbs and removed the diaphragms to check for tears or even the tiniest of holes?  (bright light)

And on reassembly, don't forget to get the indexing tabs in place.  There is one on the O.D. of the diaphragm for the outer rim of the carb, and there is one on the I.D. of the diaphragm for attaching to the slide.

Also, the white plastic ring can become loose, over time, if reused too many times.
Replacement rings are available from Bing.  Very helpful, small, family-run business:
http://www.bingcarburetor.com/


Inside diameter measured
Old Ring - 36.25 mm
New ring - 36 mm

[montmil]

Do not change jets before confirming diaphragms are good or you've replaced them.

If, as you say in your first post, "It ran perfectly.", then there's no need to suspect the jets. I believe you need new Bing rubber.

Monte

[cephas1981]

I second that.  Check the diaphragms.

[Barry]

Raised the left needle one notch (to the highest position). Checked the right needle and found it was already in the highest position.

The needles should not normally need to be in anything other than position 2 or 3.  (counting top groove as position 1 - weakest mixture and bottom groove as 4 richest mixture). One change of position has a quite a big effect on mixture and If you have to use 1 or 4 there is probably something else wrong. I'd be inclined to put all carb settings back to stock and start again from there.

Another thought given that "the previous owner re-built both carbs" - there is a small hole in the bottom of the slide which is the vacuum connection to the top of the diaphragm. You might want to check this is clear and also to check for correct slide orientation this hole should face towards the engine intake.

[Rob Valdez 79 R65]

also to check for correct slide orientation this hole should face towards the engine intake.  

If both index tabs are in place on the diaphragm, the slide should be oriented correctly.

[bubby-joe]

Thanks Barry.

Cleaned the idle jet, no improvement, will follow your suggestion re the idle mixture screw and report back.

Thanks again everybody!

Mine did the same thing over the last 2 months then just refused to idle no matter what I did.  Popped ran rough sound right so far.

Turns out my problem had nothing to do with the carbs at all but a very sloppy use of crimped connectors at the coils and the aftermarket MRK III electronic modual to sensor wiring by a previous owner/HACK, I replaced all 4 connections and soldered everything then heat shrank all of them then ran out the highway last night to fine tune the idle speed two adjustments to great running and no stalling.  It's never been so smooth and now runs a whole lot better.  Treat your ride like a boat and only use a crimp connector to get you to your soldering iron and heat shrink.....saves a lot of headaches in the end (OLD BOAT MECHANIC). Extra bonus should be better fuel economy without the annoying rough running engine. Already at 42MPG looking for better..

PS it's also a cure for wiring problems by LUCAS prince of darkness