Starfire Carb issue

[BEESY]

Hi All,

The tickover on my Starfire was a bit lumpy so I took it off and checked the jets and passageways etc. Carb cleaner flowing through everywhere nicely.

It hasn't made much difference. Tickover still a bit lumpy. But now if I open the throttle normally the engine revs up fine but if I really 'blip it' and open it to full throttle as fast as I can the engine stalls.

I assumed it was an air leak on the flange but after checking I am certain it's air tight. Ditto with the cap at the top of carb  I'm sure thats airtight too. I've even put a smidge of wellseal on it as an experiment. It's really puzzling me. The engine runs smoothest with the pilot air screw fully screwed in. When I throttle off the tickover drops to a fast idle for about 20 seconds and slows down to a normal tickover

All parts of the carb were new about 3k miles ago.  I've raised the needle a notch so now in the bottom groove of 3.  It runs a bit smoother but still stalls when I 'blip

Before I bin the carb, has anyone else had this problem before?

[chaz]

points clean. valve clearances ok?
you could try carb cleaner or easy start around the carb to see if it speeds up, would check for air leaks.
before you bin the carb, have you checked needle and jets for wear? they are cheapest bits, the body is the dearest part.

[BEESY]

Cheers Chaz.

Valve clearance ok. It's on wassell EI. Checked timing and its all good. It did cross my mind that the EI could be faulty but can't see how that would make bike run with the pilot screw fully turned in. That should make it stall shouldn't it? Plus it p it runs fine on the road. It's only really the stall on the 'blip' and lumpy tickover.

It seems to me to be air leak or weak mixture. A worn inlet valve crossed my mind but no evidence of it like smoke or fouled plug.

Everything other than carb body is 3k miles old.

[AWJDThumper]

Could you please clarify the history of the carb? Was this new 3k miles ago or was it just overhauled and the jets and throttle slide renewed etc. Also, was everything ok with the bike's running over the last 3k miles and the problem has developed recently.

Assuming, it wasn't a new carb, the big problem with overhauling old carbs is that as well as the throttle slide wearing, the slide body against which it rubs also wears. If there's too much wear even with a new slide, air can leak past especially when you create max vacuum by snapping open the throttle!

[chaz]

the carb bodies can be saved, hone out the bore and if necessary get the slide replated which will add to the diameter.

[BEESY]

It's the original body. New slide, needle, jets and float. No sign of wear at all on the slide (hard anodized one) only light scuffs in the body which were like that when I refurbished the carb.

Tick over always been a bit lumpy. I decided to make sure the carb was clean to see if I could improve it. When re-assembled tick over slightly better but not much. I have even cleaned up the flange where it joins to the barrel with fine wet and dry on a mirror.

But I also have the issue with the stalling when I open the throttle wide very quickly. If I open it normally it revs up fine. It rides fine. Plug us showing the mixture is ok. Perhaps a little weak. More grey than light brown.

The thing that really puzzles me is the pilot adjustment. Screwing it right in gets a really smooth tickover. It even runs with the pilot screw completely removed. But the pilot passageway way is clear.

Can I post video on here to demonstrate?

[AWJDThumper]

If the carb body is ok, the slide should be a snug sliding fit with no side play discernible - if this is the original carb then after 40+ years of use, there's a very good chance the carb body is worn out. If it is leaking air past the slide then you could very well get the symptoms you are getting. New carbs are relatively expensive and it's probably better to try and borrow another carb to see what difference that makes. Trying to work out why a particular carb behaves in the way it does can sometimes be a bit unprofitable!

[BEESY]

Appreciate that Chaz. Sadly no chance of borrowing one I'm afraid.

I was wondering if anyone has experienced these symptoms before and might have suggested something I haven't yet tried. I have spent about 15 hours on this so far. Removing and cleaning and checking and double checking all for nought.

Looks like a new carb. Bad news is Burlen have no stock. Has anyone tried a Wassell one?

[chaz]

Ive got a pair of Wassell concentrics on my Triumph chop, work perfect, runs with chrome short mesh filters.
the original 600's were eaten by ethanol but were running on longer trumpets with finer mesh

[BEESY]

Cheers for   that Chaz.

[MGILBERT]

Hi
I had a similar problem with my starfire , poor and lumpy tick over. Abeit didnt cut out when revved.  My problem was the Pilot Air Galleries blocked.  and noting your comments on removing of pilot jet screw  , and bike stills runs suggests cloggged galleries .
check out youtube.
amal carb pilot jet cleaning
paul henshaw

i must of cleaned my air galleries at least 5 times before i got the results of a good tickover. Hoping you will/have resovled your problems.
bfn
mike

[BEESY]

I've cleaned the pilot galleries out thoroughly 4 times. Everything seems clear. When I spray carb cleaner I get powerful jets spraying out of all of the orifices.

I have tried a bigger pilot jet 30 from standard 25. That's when I 1st noticed the stall when flipping throttle hard. Changed it back to 25 symptoms same. Have raised the needle fiddled and adjusted it for hours.

Nothing seems to make much difference. Adjusting pilot screw speeds up and slows down the tickover but its always lumpy. The slide screw is sometimes so sensitive the slightest turn makes a huge difference in tickover speed on other times a 3/4 turn makes no difference.

Its driving me nuts.

The only thing I haven't tried is blowing through with compressed air. Haven't got a compressor.

6 to 8 week delivery from Burlen for a new carb.

[MGILBERT]

Again you go down a similar path to me. When i stripped the carb i found that an oversize main jet had been fitted causing the bike to loose revs and become lumpy at 45 mph.(to much fuel)?
I then rebuilt carb with ALL new components but reverting back to factory settigs.   
Needle setting postion no 2 couting from the top.(REF Burslam) 
Main jet. 200

yes it drove me nuts as well

[JOHN KAY]

 HI THERE > I HAD SIMILAR PROBLEMS WITH A CARB FROM TR25W > PILOT JET (FIXED TYPE ) BLOCKED COMPLETELY AND WOULD NOT TICKOVER >ONLY CURE FOR ME WAS TO USE A VERY FINE SEWING NEEDLE  WHICH WONT BEND LIKE WIRE DOES > I ALSO USED A CAR FOOTPUMP WITH PRESSURE GAUGE ON IT AND A TAPERED ADAPTOR FOR BLOWING UP AIRBED > BIKE NOW TICKS OVER FINE> A BIT DRASTIC WITH THE NEEDLE SOME WOULD SAY BUT IF IT WORKS WELL FINE >REGARDS JOHNBOY.

[BEESY]

Somebody once said 80% of carb problems are electric!

It was the ignition coil after all. I had persevered with carb umpteen times. Went for a wrong ride to see what I could see so to speak.

Misfire got progressively worse and it became obvious it was the coil.