PHBG masters please help

Calvin Laszakovits /

Hey guys and girls who know their way around a phbg carb! I’ve recently upgraded to a 19mm with an 18mm intake on a polini 70cc kit. The bike is a ‘78 Garelli GranSport. Up to about 1/2 throttle, maybe a little over, it runs top, it runs perfectly. Once I hit about 40mph and am in the top end of the throttle, it starts bogging out. It usually needs a moment to recover and figure itself back out if I go into that bad zone. If I hold throttle all the way open, it bogs down, and then does a weird revving thing where it slightly revs up and down but goes real slow. I’ve tuned and returned my gas/air ration screw, set my idle jet (42), and changed my main jet everywhere between 86-94. I have the needle on the second leanest setting.

I’ve checked for airleaks, all seems to be good. Timing should be right on the mark. I have an estoril sidebleed pipe and a high flow filter on the bike. What am I missing?!

Any help on where to go from here would be amazing.

Thanks everyone!

Re: PHBG masters please help

#CrazyWayne™ rocks. #CrazyWayne /

Go look it up in the wiki

Re: PHBG masters please help

Ilia Edouardovich /

Is your ignition system in good shape? I’m not familiar with the kit (piston port or reed?), but my approach is always to use the biggest idle jet possible and proceed from there. When dialing in the idle jet I ballpark the main jet and set the needle to second richest setting on piston ports and third richest setting on reed kits (FYI I haven’t touched a piston port in many years). Check the wiki as mentioned. Maybe a different needle would help?

Re: PHBG masters please help

Did u try ( if it's a points ignition ) opening the gap a tiny bit which should advance the ignition ( make it occur more BEFORE tdc)?

Re: PHBG masters please help

if ya got a air leak behind your stator, tuning will be impossible. say, "if the carb is way up there why is it wet here, hmm".

Re: PHBG masters please help

That setup should be 43/94 jetting with and don't​ forget the W7 needle.

1) Sounds like your close so next is to check your gas cap. Is you have one of those damn female threaded on caps that's probably you problem because they swell up, dry out, clog up which in turn creates a vacuum. If that's the cap try loosening it and see what happens.

2) make sure you petcock is super clean and has a good steady fuel flow.

3) check the float level in the carb.

4) like Pat Splat said your seal behind the magneto could be going bad (this is a common problem with noi's) and needs yo be replaced.

After you have done all this report back. Also make sure you have a new spark plug. I don't care how good it fired if you lay it on the cylinder to check it.

Re: PHBG masters please help

Fuel flow.

Check your float level.

Replace the crankshaft seals always!

Your jetting seems close enough that it shouldn't be lean bogging.

Re: PHBG masters please help

No one going to mention "phbg carb! I’ve recently upgraded to a 19mm with an 18mm intake "?

Yo, Thats backwards. Intake needs to be larger than carburetor. It'll still work but tuning definitely won't be easier. If I'm thinking about the physics properly, you're going to have difficulty tuning main jet and the needle position. While opening the throttle, After you enter that extra 1mm (cross-sectional area), the pressure in the carb will drop unexpectedly. Less pressure means less gas coming up through the jet, so it'll lean out. So you can definitely tune idle (throttle slide closed) up to 3/4, but after that you enter the twilight zone.

edit: yes, this is simplified and I know the velocity of the air is also dropping. Its possible I didn't put the right terms in places.Edited 1 time(s). Last edit at 10/31/17 01:11PM by fowler.

Re: PHBG masters please help

Referencing my previous comment, Have you tested and tuned 1/2 throttle? Thats almost exclusively regulated by the needle.

did you match the cylinder intake port to the new intake?Edited 1 time(s). Last edit at 10/31/17 01:18PM by fowler.

Re: PHBG masters please help

Ryan what makes u think "lean" bogging.

Re: PHBG masters please help

> Marc Friedman Wrote:

> -------------------------------------------------------

> Ryan what makes u think "lean" bogging.

Lean means bog

Rich means four stroke or cut off

Re: PHBG masters please help

Ok I guess. Because it hits a spot where it comes off the pipe and loses the ability to further accelerate and all sorts of stumbling. Could it not be too rich or to late a spark ? And still sound the way he describes? And is bogging down. That would be what : a rich bog?

If it for sure was because it was getting too much oxygen when carb slide wide open I can understand why alot of folks assumed he has some kind of air leak.

But I don't understand how that is known.

Re: PHBG masters please help

It might be ok if you go up on the main jet and drop the needle(move the clip up). but there might be a dead spot between 3/4 and WOT.

Have a temp gauge? Maor input required. You tune the carb all day if theres some other problem you haven't found yet.

You said it was bogging in your other thread, and then you went down on the main jet, which didn't fix it. I bet you need to go up.

Are you sure its not a fuel flow problem? Is there anything in the float bowl that can sporadically clog the main jet? Water in your gas? replace fuel filter?

Bad tranny side seal will make it run hot and white smoke (instead of blue). bad stator side will just run hot.

I could keep going... but I'm not thereEdited 1 time(s). Last edit at 11/01/17 08:24AM by fowler.

Re: PHBG masters please help

#CrazyWayne™ rocks. #CrazyWayne /

LOL

Re: PHBG masters please help

Calvin Laszakovits /

Petcock is clean, float level is parallel with the ground.

Will do the gas cap check and check magneto seal!

Thank you!

Re: PHBG masters please help

Calvin Laszakovits /

One of the only things I haven’t done is the three seals. I’m willing to bet that’s my problem. Thank you!!

Re: PHBG masters please help

Calvin Laszakovits /

Betting it’s the seals. Will report back.

Re: PHBG masters please help

Calvin Laszakovits /

A looser gas cap improved the issue. I found some oil underneath where it shouldn't be as well so new seals are on their way. Thanks!

Re: PHBG masters please help

Calvin Laszakovits /

Okay, update time.

Did the seals but I believe I have another problem. It's been happening since right before I replaced the seals. I've gone over the carb several times and nothing has changed. One day it was fine, the next it was doing this. Main jet 90. I linked a video below. I can get it to low 30's if I very slowly and carefully get it there, but if I give any more throttle, it bogs. When I come to a stop, it feels like the carb is still pulling a little but the carb fully closes when I open it up and inspect it.

Re: PHBG masters please help

What are the temps please ?

Re: PHBG masters please help

Calvin Laszakovits /

Will get temps tonight or tomorrow.

Re: PHBG masters please help

problem 2 common noi clutch issue please read.

also, get a cheap jammy pipe and clamp on.

Re: PHBG masters please help

Calvin Laszakovits /

All 6 bushings are brand new and the star pattern large rubber clutch piece seems to be in fine condition. I have a brand new one I can put in. I’ve just gone over the wiki again and don’t see anything else I’m missing.

I have an estoril side bleed pipe which has been great so far.

Re: PHBG masters please help

todd amundson /

Humor us. Please put a 45 idle and a 82-83 main in there. Stick with a W7.

Just try it

Re: PHBG masters please help

Calvin Laszakovits /

This set up should be 90+, no?

Highcomp head

19 carb

18 intake

70cc polini

B8 plug

This bad running started happening without me changing anything. It ran just fine with a 90 in (except for top end which was the original problem, leading me to do the crank seals).

Re: PHBG masters please help

Mikey Antonakakis /

I am also having funny issues with a PHBG on my Peugeot, happens at 11k (should rev out to 13k+ if the carb works properly). I am at this point 90% sure it is related to float needle, I am using a clamp mount carb (no rubber boot) and I am thinking vibration is either foaming the fuel or causing the float needle not to seat and flooding the carb. It's water cooled, spark plug temperature never gets over 140F, jug is cool enough to leave my bare hand on for several seconds. I have a clear float bowl on the way to help diagnose. But basically the bike absolutely rips up to 50-55, then it reaches full variation and as soon as it starts to rev out, completely stalls if I give more than like 30% throttle, although exact amount depends on the jetting.

Re: PHBG masters please help

Mikey Antonakakis /

Sure enough, fuel is foaming and spewing all over the place, video is on its way. It gets worse the longer I ride. Did about 15min of riding with a GoPro pointed at the carb, and what do you know, hit 67mph on my first full throttle pull, still accelerating, until I came up on traffic. Foaming got worse and after a while couldn't break 55.

Re: PHBG masters please help

Calvin Laszakovits /

Curious to hear your solution, please post results!

Re: PHBG masters please help

Mikey Antonakakis /

Ha, I don't have a solution yet, but I will be sure to let you know when I do!

Re: PHBG masters please help

Mikey Antonakakis /

Probably easier to see this on a bigger screen (hard to see the bowl on a phone). Not the most exciting video, but the more I ride, the worse the sputtering/bogging/cutting out gets at high RPM, and clearly there's a wild party happening in the float bowl every time I rev up.

video: youtu.be/Ku9WgmrcBls?t=1m45sEdited 1 time(s). Last edit at 12/19/17 09:41PM by mantonakakis.

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