Hi,
Sometimes I really don’t understand why taking so much trouble and risk to get the engine running well by yourself.
My advice would be :
Get the engine running as good as you can and put it on the dyno, including a gas analyser. Find a location with an older mechanic who has experience with carburettors and knows his way on the dynojet. Within minutes he can tell you how the engine is running, and what to do.
Many people see the dynojet as a machine for increasing the maximum output power, but in good hands, the dynojet is a very good diagnostic tool.
I have seen and heard many CB72 / 77 , dreams, and other early Honda twins running, and when listening good, you hear not many engines running like they should run. They run on one and a half leg, vibrating violent, not picking up good, are not idling stable, etc. If you point that out to the owners, they only say, it’s an old bike, so what do you expect ?
I have seen many dynojet charts, and I put my machines at least once every two year (or every 5000 km) on the dynojet, and I’m always amazed by the info you get back from it.
A lot of people here on the forum are spending a lot of money on paint jobs, chroming, NOS parts, etc. Why not spend 50 to 150 USD to get the engine running well ? In the end, a healthy running engine, synchronized and not to lean in any region, will save you a lot of money on engine parts.
I thought I never could get it out of my mouth, but a good and health running engine is more important than the kind of oil you run in it. If an engine is running lean or one leg is not running 100 % it will destroy pistons no matter what oil you run in it.
There’re a lot of things that someone can do yourself, like points, timing, float height, oil filter, changing plugs and do regular maintenance, but setting up the carbs is specialized work, and is in better hands of very experienced people. Watch them, look what they are doing and learn.
There are only a few people on this forum who can get these machines running good without any help from modern techniques. They can do this because the experience they have is far beyond anyone can imagine (even themselves). Even if you follow the recipes and hands on information on the forum, it still is very difficult to do that.
A good “dyno man” can “read” many things from the results, from synchronisation to a worn chain,
Jensen
eyhonda - 63 cb77 cafe project
Hi Jensen:
Well, I don't think it's a lot of trouble. I think it's part of the charm and I would call it tinkering. I learn a lot by messing around with it myself. But, I see your point. There does come a point when tinkering around too much will become trouble. At that point, I'd rather just start it and ride. Plus, the better it runs, the more I will love riding it. I will call around for the local dyno guy as soon as I can. But at what level will they analyze the problem? Will they just point out which carb is lean or will they tell me exactly which part of the carb or carb area is causing a condition (jet, needle, jet holder, slide, etc)? I've never been to a dyno guy. So now I'm curious. Tell me more. 63 cb77 cafe
www.eyhonda.com
I'll have the local Honda guru take a look at it. Phil bored the cylinders and did the valve work. All of them at shop is curious to see my bike anyway when it's done. I'll pay them a visit on it's maiden voyage (when it's street legal).
63 cb77 cafe
www.eyhonda.com
Hi,
First of all, I wrote this mail in general, not to you as a person, but indeed, it ended up in your thread. I just can’t understand why not going to a specialist and spend some money to get it running good, and at least not to lean. A dyno guru would possibly do the following : First he looks at the bike in general, and listens to it, followed by a compression check and a timing check (these things you can do yourself). Then he will open up the float bowls (make sure your packing’s are in good condition) and check if the jets are clean (and blow them with pressed air), the floats are not leaking and the float valves are working. He also will look if the float heights are the same and according to specs and check that the needles are the same, and on the same clip. It’s best to take the specifications with you, also the sizes of the jets and the needle position etc. If the bike found to be good enough, he will proceed, if he already finds problems here, he will ask you to fix it (leaking carbs, leaking exhaust system, not enough compression, etc.). If anything is wrong at this stage, there’s no point in going further. A good specialist will do these things, no matter what you tell him that you did that already. If you did check and fix above things he will be ready within 20 to 30 minutes. Until this point a lot of people are able to do that at home, depending on there experiences (the ED Moore recipe) After that he will warm up the engine and idles the bike for a while, checks if the temp on both exhaust pipes are equal, and put in the gas analyser to see how the combustion is per cylinder. Then, per cylinder he will try to make the mixture combustible, and after this he will make the carbs equal and synchronise them. This is an iterating process, and will take time. I made vacuum measurement pipes on the carburettor manifold to make this process going faster and easier (like modern bikes), so vacuum gauzes can be attached. If he doesn’t get the basics right he will give you possible reasons why, so you can act on this (for example the advance mechanism isn’t working properly or something else isn’t right) If he gets the basics right he will put the bike in gear to proceed to the point where the needle takes over from the stationary rpm’s. This is the region between 1200 to 4000 / 5000 rpm and he will check if the engine picks up good by opening the throttle. At this point the rear wheel is spinning on the dyno, and the gas analyser will tell him if the engine is lean or rich and if both cylinders are working together. He will also change gears, but staying in this region from idling and picking up. If necessary he will change the settings of the carbs (needle, air etc, float height etc.) This is also an iterating process, and if things will come up, he will first get it right (for example a worn needle or needle yet). After that he will do a few full runs to see if the main jets are good, and change them if necessary. He also checks if the clutch is working good, if the transmission is good (if it is shifting properly and many other things)After this session he will discuss with you, what he thinks of the engine and how it’s running. Try to find someone that will let you see what he’s doing, and learn from him, try to understand what he is doing and why, and ask questions. The first time is also a learning process of the man on the dyno, becuase probably this will be his first hawk or superhawk on the dyno. Make sure you agree before the process what the cost are, or how much time he can spend on the bike, or what you will do yourself. Jensen assembly of Japanese motorcycles requires great peace of mind (Pirsig)
forgot to ask if ya had hose on the brass tubes on the carb bowls.
If ya do remove them and ride to see if this helps. HONDA didn't put hose on those brass tubes. ...............lm
I have yet to pull the plugs. Letting it cool. But it runs good now from idle to 6k where I have to slow down. Yes, I don't use hose. It still pops a little under heavy throttle and above 6k but it might be a jet or a needle issue at that point. My Honda guru doesn't have a dyno. Probably tunes old school methods. I'll shop for a dyno guy tho. Sounds like a good investment.
63 cb77 cafe
www.eyhonda.com
Scott, they are very accurate, showing the 'live' combustion colour at the current air/fuel mix. I've not used mine since the '70s. And it's for 14mm plug 'oles. And it's somewhere amongst my shite in England, probably at my sister's! 44ccs in mine.
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||