Carb setup LM1

SBD

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I stripped, ultrasonically cleaned, painted & rebuilt my (PHF36) carbs using the Dell’Orto refurb kits. I’m reasonably sure that I put everything together correctly, and the bike runs, but it’s not right. Before I strip the carbs again, I’d appreciate any experiences or pointers anyone can offer.

The plugs are black (right) & black /wet (left) so it’s obviously stupidly rich.

It’s idling on the right cylinder, the left fires occasionally, it starts when cold, it will start when warm if I don’t touch anything other than the starter button. Opening the throttle it picks up on both cylinders & revs freely, but starts popping & banging at constant throttle & 5k rpm. Don’t want to do that too much, we have nice neighbours and I’d like them to stay that way.

When idling, the left carb adjuster screws make no difference, the engine does change with the screws on the right carb.

There is slack in the “choke” cables.

The throttle cables are approximately synched, I haven’t put the vac gauges on it yet.

Tappets are correct, timing is also good.

My thoughts are

1 float valves not seating (I don’t think they included new ones in the kit, so I presumably put the old ones back in)
2 floats set too high, causing flooding (or at least incorrect fuel level)
3 I’ve reassembled something wrong

Gutsibits didn’t have float valves in stock, but Beedspeed did. Will fit them and double check the float levels when I take the carbs off again :(

Any other ideas?

Ta
Simon
 
Sounds a bit like a blocked passage somewhere to me. Take them apart again and ensure all the passageways are actually clear by spraying in carb cleaner and checking it comes out the other end.

Check the float levels, but IIRC the levels in the Guzzi manual are wrong anyway. i've got a note of the correct height somewhere. I'll try and remember to look it out.

One tip I was told by someone well versed in these bikes, is that the tips of the float needles expand over time throwing the levels out. I checked and it had happened on mine. Didn't solve the lean spot in my midrange that appeared for no reason where it had been running fine for the previous 25+ years. I had to raise the needles to fix that.
 
Have you checked your spark timing with a strobe?

DAMHIK …

I spent weeks chasing a carb problem that was an ignition problem after all. And no it wasn’t just me, I had advice from the Guzzi tech gods as well.
 
If it’s only the left hand carb then I’d suspect either a blocked passageway or leaky float needle. Ultrasonic cleaning won’t clear a blockage best use an airline.
 
Thanks both.

I haven’t timed the bike in probably 13 years, as it has a Rita setup which has been truly fit & forget. It’s worth checking, but the only thing that has been fiddled with is the carbs, and the wet & black plugs seem pretty clear evidence, so I’m pretty convinced that’s where the issue is.

I thought I’d checked the passages as I rebuilt them, but maybe I missed something. They’re going to have to come off again anyway

Ta
Simon
 
Definitely sounds like blocked pilot circuit re the idle. Some of the drilling’s are tiny and need cleaning then re cleaning followed by a bit more cleaning:D I sometimes use a bristle off a wire brush or actually unravel a copper wire:eek:
 
painted carbs ?

timing , reset it , as chain wears ...timing goes out .

tappets good ?? what does that mean ? 0.20mm inlet and exhaust

plug caps resistance , check ....5k ohms , replace if needed.

is it sparking , check while you have caps off.

do plugs spark ? change plugs ....

---- carbs -------

strip completely clean again , blow thro' with carb cleaner and air

choke plunger rubber, at the bottom , still there ? is it sitting all the way down , or is jet damaged where they touch ?

fuel float is it full of fuel ?

fuel inlet needle , test with thumb nail for give.

fuel level , i set bottom of float to match bottom of pilot jet.

***the tickover screw not responding says to me timing....***
 
My float was sticking on my Cali' 3 with the same carbs. Float wouldn't swing on it's pivot. Don't know if its the ethanol in the fuel that messes with the plastic float. I filed a little bit of the ends, where the pivot pins go. Might be totally irrelevant, but, it's an easy thing to look for and free to fix.
 
Thank you for the extra recommendations, much appreciated.

New needle valves due tomorrow, so the carbs are coming off and to bits again.

Yes, I painted the carbs. Only on the outside... They were already painted, I thought it was original, but perhaps not.

Tappets were set to 8.5 thou about half an hour before I started it.

Timing is as it was when I left your place after you did the clutch Christmas a year ago. It ran before I took the carbs off, I’ll happily re-check it but I don’t think it’s the reason. Who said all carb problems are electrical?

Yes, it is sparking, though I’d have preferred a big fat blue spark to what I’ve got. Rexspeed Rita replacement ready to fit.

I do have slack in choke cables, the plungers go down fully, I have not checked whether the choke jets are damaged.

I shall redo the carbs, ensure every drilling is clear, check the chokes, fit new needle valves, verify the float height, make sure the floats are not sticking anywhere, put it all back together and see where we are. I’ll measure the plug cap resistances, I already tested the coils. The plugs look ok when I clean them, but I’ve got a spare pair, so I’ll throw them in too.

Assuming all well, actually, assuming it’ll run, I’ll strobe the timing and adjust if required. Once that’s sorted, I’ll vac synch the carbs.

Should keep me occupied over the weekend.

Thanks again
Simon
 
Don’t change the plugs until you’ve tried the carb after rebuilding. I’ve had these types of faults before and dived in there, changed everything I can think of all at once, fault goes away but I’ve no idea what was causing it!
 
Thanks JJH, BUT It’s a LeMans, you can see through the “air filters”! They’ll keep bumble bees out, but that’s about it.

But yes, under normal circumstances, I’d agree entirely: daft rich - check the filter first cos it’s quick & cheap to take out.

Thanks again
Simon
 
Strange goings-on.

I took each carb off, and changed only the fuel filters & float valves. The ones that were fitted had two fibre washers, I put the one new one in.

The old needles had black rubber tips, the new ones are red.

I checked the float height, maybe marginally under 18.5mm.

I poked out the jets with a strand of wire, just to check, tho’ I was confident they’d be ok. Blew compressed air through the carb passages too.

Double checked that the chokes are seating down. I have new plungers, but haven’t fitted them. It whistles when the choke is out, and doesn’t when it’s not, so I think they’re sealing. Easy to change later anyway.

Reset the idle mixture screws to 1.5 turns out, and got it to start. At this point, it was running on the left cylinder, but not the right one. This is a curious reversal of the situation last weekend.

Now, something I’d forgotten, when I was tidying things up, I changed many of the screws for stainless, and I painted some of the bits of steel around the battery tray. I wonder if I had somehow failed to ensure the ignition system earth connections were good enough, so I made up a lead to connect the earth point back to battery negative. This certainly seemed to help.

Well, it was running, but not happily, until I covered the intakes, one at a time, with my hand as I opened the throttle a bit, which led to some serious spitting and coughing, and some quite big flames from the exhausts, and it then settled down to idle quite nicely. I wonder if I had an air-lock in one of the carb passages. I wonder if I had an airlock in the other carb before.

It’s not right, but it’s much better. It starts off the button, choke if cold, gentle twist of the throttle if warm, and runs evenly on both cylinders, not yet idling without slowly puttering out, but it’s now useable..

Then I checked the timing. If the indication on the strobe is to be believed, it’s about 60 degrees out. That can’t be true. Puzzled.

Well, I wouldn’t want to be bored tomorrow.
Cheers
Simon
 
Then I checked the timing. If the indication on the strobe is to be believed, it’s about 60 degrees out.

There’s your Huckleberry, right there.


Sent from my iPhone using Tapatalk Pro
 
Not sure how you see or measure the timing is that far out, whatever there’s a good chance that that is your problem - turn the ‘distributor’ to get itsomewhere near and I suspect it’ll run a lot better.
 
It’s difficult to believe that it is possible for it to run with timing that far out. Need to get to the bottom of that.
 
My strobe is a Gunson purchased at great expense (£54.99!) from Halfords some thirty years back. It has an advance adjuster knob on the end. It’s so long since I used it I have no idea whether it retards the flash or advances it. In any case, with the bike on fast idle at around 1500rpm, and the pickup on the Right spark lead, turning the knob leads first to the S mark appearing at about 30 - 40 degrees and the D at around 60. Given that they should be 90 degrees apart, it’s perplexing to say the least.

Taking Baldrick’s comment about the timing drifting as the cam chain wears, and other comments about the timing, and what I’ve read on other forums, I’m going to dead-stop time it. I’ll laser cut a timing wheel and fit it to the alternator, remove the plugs and fit a dead stop to the right cylinder. That will allow me to turn the engine forwards to the stop, backwards to the same stop, and thereby accurately locate TDC (apparently the factory marks are “there or thereabouts”) and thus the target full advance point. I’ll centre-pop & paint-mark the flywheel to give myself a check for the future.

I can then fire it up and strobe it at 6500 which is full advance for the Rita, and we’ll see where we are then.

Cheers
Simon

A silver version of this
https://www.gunson.co.uk/Product/77008/Timing-Light-with-Advance-Feature
 
Did a bit today, despite the crappy weather.

Firstly, finding TDC. The recommended approach, using a timing wheel on the alternator end of the crank, and dead stops in one cylinder, did not work quite as planned. I had a bit of an issue laser cutting a protractor, finally fixed that, took off the alternator cover and looked at fixing it to the crank. It’s a special bolt... So I made one, with an extension on which to mount the protractor, fixed by an M8 nut. Tightened the nut, and the plastic protractor exploded. The dead stop isn’t a great idea either. The angle of the spark plug to the axis of the cylinder means that rather than simply gently stopping the piston dead in its tracks, it simply bends the stop. I suppose I could have made it tougher, but it seems like a better solution is called for. I put an insulating sleeve in my modified spark plug, and slid a length of piano wire through it. A multimeter show when the wire touches the piston, and some fiddling proved that the D & S marks are one tooth out. I marked up the 9th tooth before the corrected TDC for both sides, and if the weather permits tomorrow, I’ll be able to strobe it and hopefully get something sorted.

First, static check. Well, the timing hadn’t “drifted”, but the screws that fix the reluctor baseplate to the distributor were loose. Fixed that and regapped the reluctor from the cam. It looks like they hadn’t touched, despite the screws being loose, as the cover prevented the plate moving much, but I’d bet it had moved a bit. Well, it’s tight now. Fit & forget, but only if you put Loctite on the screws...

I had the tank off to do the distributor adjustments, so I couldn’t run it, but gave it a prod and it fired up straight away, so that bodes well. More soon.

Cheers
Simon
 


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