PHBL 25 pilot jet advice please

[Pompeydave]

Evening all, I’ve got an Allstyles 186 kit with a Dellorto PHBL 25 carb. I can’t quite get it to tickover even with the adjuster wound right in. The pilot is a 53 size. Can anyone recommend an alternative size to deliver a bit more fuel please?

The main is a 95 by the way. It’s been dyno’d by Johnny Gilbey at the IOW last year and it runs nicely with a chocolate brown coloured plug after a good run.

[Storkfoot]

Until 12 months ago, I had no experience of the PHBL25. I have now set two up, one on a Stage 4 200 and one on a Casa 185. My experience has taught me that the mixture screw has a significant impact on tickover.

The Casa 185 runs with a standard GP200 mushroomless exhaust. I have a 48 pilot and tickover is spot on. What exhaust do you have?

[Pompeydave]

Hi Storkfoot, running a BGM big box mk3. Very conservative timing at 16 BTDC. No air filter, just run it through an empty air box.

[hullygully]

why 16 deg btdc bud?

[Storkfoot]

Hi Storkfoot, running a BGM big box mk3. Very conservative timing at 16 BTDC. No air filter, just run it through an empty air box.

Each engine is different but, given your set up compared to mine, you probably need a bigger pilot than a 48 but smaller than a 53. If you have to screw the air mixture screw in, you are weakening the mixture and, if it still won’t tick over, it’s worth trying a smaller pilot, say a 50 or 51.

Then warm the engine up properly and spend some time adjusting the air mixture screw, listening to whether it likes being richened or leaned off. Also, look at the smoke coming out of the exhaust and whether, whilst blipping the throttle to no more than 1/4 throttle, the engine responds readily and doesn’t hang up when coming back down to a closed throttle position.

This is, of course, assuming that you don’t have a small air leak.

[Pompeydave]

why 16 deg btdc bud?

Just wanted to run it as unstressed as possible. Might be overkill, but it has run for thousands of miles and done some long distance trips to Whitby, Woolacombe and Ladram Bay without ever coming close to a seize.

[Pompeydave]

Hi Storkfoot, running a BGM big box mk3. Very conservative timing at 16 BTDC. No air filter, just run it through an empty air box.

Each engine is different but, given your set up compared to mine, you probably need a bigger pilot than a 48 but smaller than a 53. If you have to screw the air mixture screw in, you are weakening the mixture and, if it still won’t tick over, it’s worth trying a smaller pilot, say a 50 or 51.

Then warm the engine up properly and spend some time adjusting the air mixture screw, listening to whether it likes being richened or leaned off. Also, look at the smoke coming out of the exhaust and whether, whilst blipping the throttle to no more than 1/4 throttle, the engine responds readily and doesn’t hang up when coming back down to a closed throttle position.

This is, of course, assuming that you don’t have a small air leak.

Actually, now I look at the plug again it’s a bit darker than it should be so I think it is running a bit rich. I’ll try a smaller pilot jet and report back.

[Pompeydave]

Looked at the needle today as I was thinking it might just need raising up a clip to push the needle further into the body. Turns out it’s already on the top clip! It’s a D22. Don’t know what to do next. Weaker needle? It’s clearly running too rich as it is currently set up and I still can’t achieve a tickover even with the throttle screw wound all the way in.

[Pompeydave]

No one got any thoughts on this?

[Storkfoot]

I’m a bit confused. Your opening post said it was running okay except it didn’t tick over. Are you now after jetting advice throughout the whole throttle range or just tick over ?

[Pompeydave]

Sorry, it’s a combination of both. It’s running rich I think as the plug is a bit darker than it should be. It also won’t tick over.

[Storkfoot]

Are you doing proper plug chops or are you just taking the plug out at the end of a run after you cut the ignition at idle? If it is the latter, all you are getting is an indication that your pilot jet/ air mixture screw setting may be too rich.

Putting aside the inability to tick over, if the engine runs well, the exhaust is not too smokey, there is no black sludge at the tailpipe end, the engine revs up and done well without “hanging up” when you are coming down off the throttle, you have not had any seizures, there are no noticeable air leaks, I wouldn’t worry unduly about the plug colour being a bit dark.

Going back to tick over, have you tried a smaller pilot jet yet, leaving all your other jetting as it was before?

One last question, when it went on the dyno, was it just to see what power and torque it put out, or was it to do a proper air/fuel ratio analysis to change the jetting accordingly?

[Pompeydave]

No to be fair I’ve just run it for the rally season and got it on the ramp to do a few maintenance jobs. I took it from Pompey to Whitby at Easter and it ran aok all the way there and back. I just took the plug out to renew it and on closer inspection it just looks more sooty and black than chocolate. I’ve not tried plug chops but think it would help so I will do them as described in other threads I’ve seen.

I’m running a 53 pilot currently so I’ll source a 50 to see if that helps the tickover.

The bike had a proper two hour air/mixture analysis but I asked if it could be set a little rich as I’m doing a lot more long distance rallies now. I haven’t changed anything else other than to adjust the slow running screw.

Thanks for the ongoing advice, much appreciated.

[Warkton Tornado No.1]

I’ve been following this thread & I think you’ve had the best advice, which you may now follow in trying smaller pilots. It’s worth shopping around, but this may help:

https://justlambretta.com/product/bgm-p ... -pcs-kk27/

Looking at their prices for atomisers, worth getting new - along with the needle, though price unchecked - & save a bit on cost of P&P

Just don’t make too many changes at once

[Pompeydave]

Thanks. Are the BGM jets a good copy of the Dellorto originals?

[ULC Soulagent]

Thanks. Are the BGM jets a good copy of the Dellorto originals?

No, use KMT

[Pompeydave]

Ok, thanks.

[Warkton Tornado No.1]

I have no idea of the accuracy of the jet packs from the likes of BGM but the principle of procuring packs of jets to dial in a carburettor is one that I have adopted for other makes of carburettor. The whole set, whether it be Polini, Stage6 or whatever, will get you in the right ballpark by using the set as comparators. The additional bonus of the convenience of a tidy set is also one of the factors that I like.

You have to ask yourself whether - having ridden a machine for some time incorrectly set up - whether the precise accuracy of a pilot jet is paramount or whether the convenience a set offers is more important & constructive in optimising the carburation…….

[Pompeydave]

Yep, fair point- £17 buys a pack of 10 KMT jets in any one of 20+ size ranges, and will give me a much better chance of getting the pilot right. Think I need to do more though from what everyone’s suggesting. Seems to be running very rich even with the needle on the top clip I.e. pushed as far into its tube as possible to limit fuel flow.

[Cgt75b]

Any updates on this issue?