powerjet carburators

[jensen]

and more pictures

[jensen]

and more :

[davomoto]

Ed, yes that is exactly what I see! Aluminum cap, with a main jet threaded in. Handy for replacements I'd guess.

[LOUD MOUSE]

Ya that is what HONDA did with the CL72 carbs and as far as I know didn't do with any other bike carbs. ...........lm

Ed, yes that is exactly what I see! Aluminum cap, with a main jet threaded in. Handy for replacements I'd guess.

[LOUD MOUSE]

PIC 5...???????????????
Your chose but I assure ya that these type carbs do vent to the upper body. (all of them)
Please get away from (correct me when I’m wrong Ed).
Be correct in mind and facts as ya make statements which ya think/feel may not agree with the knowledge I share with this forum.
Am I a challenge to ya??????
I will say at this time that ya seem to take issue with what I say/offer from what I have in hand and my many years of greasy hands and paper knowledge so often that I will STAND BACK and observe how may times ya can/will solve the simple questions required.
GOOD LUCK SPORT!!!!!!!!!!!!!. ..............LM

Hi,

A few months ago while testing three sets of powerjet carburetors (CB72) on the dynojet, I noticed that seemingly identical carburetors performed very different.
A quick look didn’t reveal any differences other then the main jet, but that couldn’t explain the differences I measured.

There’s not much written about the powerjet carburetors , not on the forum, and in Bill’s Bible. The only thing I could find is that the powerjet system sucks fuel directly from the bowl and works in the higher rev regions.

I tested a early set of powerjet carbs (round float bowls) used in 1961 and 1962, a “early” late set of carbs (square float bowls ), used in 1962 and a “late” late set of carburators (square float bowls and a fuel tap screw underneath the bowl), used in 1963 and on (correct me when I’m wrong Ed).

The round bowl set gave a good performance, mixture a little lean in the low mid end (2500 to 3500 rpm), and a good higher region mixture (7500 to 10.000 rpm). The “early’ late set showed about the same results, but the “late” late set showed a very different graph. The overall mixture was a little to rich, but in the higher rpm regions it was on the lean side.

I compared all these carburetors closely and found out that one set CB72 carburetors with powerjet pipes have "closed" powerjet jets. The powerjet system fuel jet was closed and the powerjet system air jet was closed.
That means that everything is there, but it won't work. First I thought that the jets were clogged later I thought that someone closed the jets on purpose, but it seems to be a factory change.

It also appears that the carbs with a fully operational powerjet configuration have a 100 mainjet and that the carbs with the closed powerjet system has a 110 main jet.

All runs were done the same day, thus atmospheric differences were not the reason. All runs were made with identical mufflers (early stainless mufflers) on the same engine, on the same bike.

Can anyone confirm these findings ?

Jensen

[jensen]

Hi Ed,

I won't answer simple questions, the answers are all over the forum. If people are too lazy to use the search button, or dive into the problem more accurately, or don't want to spend more time looking for answers then they are at there own (that's my opinion).

If I spend more time to write down answers, then that people spend time to use the search button to find the solution, I'm doing something wrong.

Years ago people invented books to share information so that they don't have to tell everyone time and time again. And if people buy a hawk or superhawk or a dream but don't want to invest in decent literature like parts manuals, Bill's Bible's and the original Honda literature they can have it there way. Now the INTERNET takes over, and again, if people don't dive into the information, displayed on this forum, they can have it there way.

This forum is a wealth on information, and almost everything is said once or twice or more times (a lot of your contributions), I see it as a duty to expand that information, to get a more complete picture. There's where the challenge is, and most of the times I meet you at the borders of this knowledge. You could look at that as a compliment to your skills and knowledge.

There are a few people who know so much about these bikes and Bill Silver is one of them. I don't know why Bill Silver isn't on the forum anymore, he wrote a lot of good things but won't defend this information in public.

The only way to expand the information on the forum is to challenge the borders of it and you happen to be there all the time. Maybe that's why you think you are challenge to me, but believe me, it's nothing personal.

It would be a loss for many people (including myself) if you would stand back or retire but I cannot stop you doing that.

I don't need luck to answer all the questions from newbies about points, timing issues and paint colors. Everything is said and done about these subjects, so I won't respond. But if people ask question that reach the borders of this forum I will be there as I tried to be there in the past.

btw, pic 5 shows the pipe, but the late square bowl carburetor doesn't show a bleed hole. I brought the carburetor to someone with a ultrasonic cleaning device to see if it's clogged or if it's factory closed. Both carbs in the set are closed. It's just like the powerjet jets in the pictures, it's to nice to be a persons job.



Jensen

[teazer]

Jensen's findings are interesting.

The CB72 I restored a couple of years ago had square floats and Powerjets, but the carbs didn't necessarily come with that motor, so I'm not drawing too many conclusions from that sample.

The post piqued my interest so I checked out my stash of carbs and also checked the parts books. I only had 305 carbs and ones stamped B have square floats and had the castings for powerjets but no drillings and those marked CL77 did not. In addition the CB carbs had chrome plated brass slides and the CL had anodized aluminum. My assumption was that the two sets of CL carbs are later production.

The set of CL carbs on our CB160 racer also has no provision for power jets and has anodized slides. The odd thing is that I have never owned a CL, so I'm not sure where I got all those CL carbs.....

So I checked the parts books and Shop manual.

My early parts book with old style numbers shows round and square floats as if they were interchangeable and both are shown as being fitted since job 1. It does show the main jet, Power jet air jet and PJ Fuel jet, but shows them all as the same #30 in the illustration.

Later CB72/77 parts books do not have numbers for the powerjets. They are in the illustrations but no reference to the part numbers. It's as if Honda wished to forget them.

Jensen, did you check the sizes of the main air jets in all those carbs? It is possible that Honda changed the pressed in air jet to try to tilt the power curve slightly. If not I guess they just went up a size on the mains and ignored the slightly rich mid range.

I'd guess there was probably a Bulletin issued back in the day when they dropped the PJ system.