You still need to see if it squirts, the diaphram is only part of the system there is a check valve in the bottom cover that likes to stick from anything that settles in the bottom.
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Modest '78 CB750 Build
- Thread starter Pabeye
- Start date
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- Tags
- build build thread cafe sohc
Pabeye
Older than Dirt
Roger that!
Pabeye
Older than Dirt
UPDATE: A friend said it might bad fuel ( a LONG shot I agree) so I drained the fuel tank and put in new gas along with carb cleaner and she showed no noticeable improvement. Still did not want to idle or run smoothly, still backfiring and coughing.
So, I took the air filter pods off and put the stock air box back on & the bike ran decidedly better. I did not put the stock exhaust back on because it's just too much of a pin in the butt. Then just to make sure I took the stock air box off and ran it for a very short time with no air filter at all. She ran rather poorly with that configuration
My conclusion is, as most folks have said, it's running too lean with the pods and 4 into one exhaust. I have ordered a main jet kit with the following jets 110 ( which I THINK is what is in there now) 115, 120 and 140. ....which one to try first??
Also.....do I need to change the idle jets too? they are pressed in.........is it a bugger to change those?
So, I took the air filter pods off and put the stock air box back on & the bike ran decidedly better. I did not put the stock exhaust back on because it's just too much of a pin in the butt. Then just to make sure I took the stock air box off and ran it for a very short time with no air filter at all. She ran rather poorly with that configuration
My conclusion is, as most folks have said, it's running too lean with the pods and 4 into one exhaust. I have ordered a main jet kit with the following jets 110 ( which I THINK is what is in there now) 115, 120 and 140. ....which one to try first??
Also.....do I need to change the idle jets too? they are pressed in.........is it a bugger to change those?
Pabeye
Older than Dirt
Pulled the carbs on the bike today in order to install bigger main jets. You may recall it was running poorly lately. In the process I had to pull the fuel line of course.....the fuel filter I put on was buried between the carb bodies so it was very difficult to see. Take a look at the photo........note the bottom of the filter is filled with a lot of CRAP! I think I may have found much of the problem.
So, I've already changed the jets on the carbs.....went from 110 to 120........there was another option as the jet kit came with a 115 and a 140 also. If the clogged filter was the main problem I'm wondering what the best course of action is. The carbs are still off the bike.
So, I've already changed the jets on the carbs.....went from 110 to 120........there was another option as the jet kit came with a 115 and a 140 also. If the clogged filter was the main problem I'm wondering what the best course of action is. The carbs are still off the bike.
amc49
CB750 Guru
Stay with 120, change or clean the filter. If they run ethanol in your fuel be advised the gas in tank can go bad in as little as a couple weeks with the right weather and storage outside or unheated garage. Old school fuel tanks are steel and vented, air aspiration from temperature changes breathes air in and out of tank; it carries water and the ethanol condenses that into the fuel.
Bike should idle with airbox off just like box on, the airflow there is low enough so that airbox really should have no effect until the airspeeds go up from carbs opening up. They are 99.9% closed at idle. I've test run my CB550 a bunch with no box on it and it runs fine.
Bike should idle with airbox off just like box on, the airflow there is low enough so that airbox really should have no effect until the airspeeds go up from carbs opening up. They are 99.9% closed at idle. I've test run my CB550 a bunch with no box on it and it runs fine.
Pabeye
Older than Dirt
Drained the tank......not an easy process as not much fuel was coming out of the petcock. Pulled the petcock, and there was no "pre" filter. HOWEVER the "O" ring that seals the petcock to the tank was falling apart and clogging the passage of fuel to the carbs. Inspected the inside of the tank as best I could without a nifty inspection camera. There are some rust spots, but nothing really flaking and falling off.
Put new "O" ring on the petcock, tested the tank with pressurized air and all seems OK. When time permits will put back the carbs, with the pods and the 120 main jets. ( what the hell I already installed them! ) Updates to follow providing the weather stays warm!.....AMC 49...........THANK YOU for your input and advice!!!
Put new "O" ring on the petcock, tested the tank with pressurized air and all seems OK. When time permits will put back the carbs, with the pods and the 120 main jets. ( what the hell I already installed them! ) Updates to follow providing the weather stays warm!.....AMC 49...........THANK YOU for your input and advice!!!
Pabeye
Older than Dirt
After installing the new 120 jets putting on a new fuel filter I put the carbs back on and took a short drive with no pods and no air box ( I was being lazy) Bike ran poorly, more or sell same issues but somewhat better when I got on the throttle.
Then I decided to put on the air box and went for another short drive. It ran much better accelerated REALLY well and Idled pretty well too. Still getting some backfiring though. Pulled everything apart again and looked at the plugs ( see attached photos ) plugs are numbered from left to right with left one being on the left.
Keep in mind the plugs were never synched. Suggestions?
Then I decided to put on the air box and went for another short drive. It ran much better accelerated REALLY well and Idled pretty well too. Still getting some backfiring though. Pulled everything apart again and looked at the plugs ( see attached photos ) plugs are numbered from left to right with left one being on the left.
Keep in mind the plugs were never synched. Suggestions?
Medyo Bastos
CB750 Addict
a little food for thought. cheap emgo pods are, well, exactly that, cheap. K&N pods are like night and day! No more funky sucking noises, or lean popping when passing a semi truck on the expressway!
Pabeye
Older than Dirt
I hear ya, and that is why I reverted back to the stock airbox when I did the test run. I don't trust my cheapo pods either.....
Also it was not a "proper" test run before I pulled the plugs, it was just a short ride, 3 miles or so around local streets. But I was hoping to at least get an "indication" of what was going on. Frankly I can't see running the bike properly and then pulling over to the side of the road to do a "proper" test.....
Also it was not a "proper" test run before I pulled the plugs, it was just a short ride, 3 miles or so around local streets. But I was hoping to at least get an "indication" of what was going on. Frankly I can't see running the bike properly and then pulling over to the side of the road to do a "proper" test.....
Medyo Bastos
CB750 Addict
You will need to do proper plug chops to get your 3 circuits set right. Otherwise you're only pissing in the wind
Pabeye
Older than Dirt
YEP, but right now I think it's too darn cold for this old man to do that.........
are the rubber intake boots between the head and carbs in good shape? Seem like a lot of difference in color between all the plug colors. At this point you will have to get a new set of plugs to see how they turn out, the plugs you have now will never give you an accurate look at how the jetting is. Again....use the choke to determine if you are rich or lean, if it bogs down more when you start to close the choke you are rich, if it starts to pickup and run better then you are lean. You can do this at different throttle amounts to get an idea of how the jetting is at different points, this will help to determine if you need main jet changes or if you have to do some needle shimming. Also verify float levels and sync the carbs before going any further. You have to get the basics set correct before you start messing with the jets. Engine condition and ignition system condition will have an effect on how it runs and this needs to be spot on first or you will never find correct jetting.
Pabeye
Older than Dirt
DirtD.........thank for your reply. The carb boots are not cracked and appear to be in pretty good shape. The plugs are correct and new, I installed them myself and only have about 200 miles on them. The resistors are also new NGK. Now that I have all the plugs pulled I'm going to check the valve clearance and timing.....
Lets just say the #1 carb is running too rich as indicated by the black sooty deposit......How would I go about leaning just that one carb? Thanks..........
Lets just say the #1 carb is running too rich as indicated by the black sooty deposit......How would I go about leaning just that one carb? Thanks..........
If only one carb is running rich then you have an issue within that carb, be it high float level, plugged air passage etc. Or you have a mechanical issue in that cylinder...low compression. All carbs should be jetted the same, same pilot jet, same main jet, same needle height. Do your valve clearance check but you need to do a compression test on all 4 cylinders. Dont go any further till you know the engine is healthy.
Pabeye
Older than Dirt
Roger that DirtD........Thanks as always!
amc49
CB750 Guru
'...cheap emgo pods are, well, exactly that, cheap. K&N pods are like night and day!'
Really. I've run them both and both make same noise and work equally well. I have run the foam UNI as well and they work great too. I currently use APE which are K&N clones at 1/2 price, I loathe how K&N got famous and tripled prices 5 minutes later. They certainly run no better and I for one refuse to get ripped off by their incredibly high prices.
Backfire is commonly a loaded up plug to foul spark down the side of it. A weak ignition say bad plug wire or connection can make a plug look just like it it running rich. Are all plug gaps the same and to spec?
Like said, so many buy bike that has dead motor in some way (they ARE 40 years old after all!) and then pull hair out trying to find the issue when it runs like crap. ALWAYS start with a known good engine, the compression has to be a good running number (putting your finger over the hole as a test shows how incompetent you are there) before going anywhere else.
So don't listen...............you WILL eventually.
Really. I've run them both and both make same noise and work equally well. I have run the foam UNI as well and they work great too. I currently use APE which are K&N clones at 1/2 price, I loathe how K&N got famous and tripled prices 5 minutes later. They certainly run no better and I for one refuse to get ripped off by their incredibly high prices.
Backfire is commonly a loaded up plug to foul spark down the side of it. A weak ignition say bad plug wire or connection can make a plug look just like it it running rich. Are all plug gaps the same and to spec?
Like said, so many buy bike that has dead motor in some way (they ARE 40 years old after all!) and then pull hair out trying to find the issue when it runs like crap. ALWAYS start with a known good engine, the compression has to be a good running number (putting your finger over the hole as a test shows how incompetent you are there) before going anywhere else.
So don't listen...............you WILL eventually.
The half price pods from Dynoman work just as well also. i agree K&N are not worth the money for what you get...the name.
Pabeye
Older than Dirt
Thanks Dirt, as always.
Here's a question unrelated to carbs and motor health, hopefully avoiding any further rude remarks by a self proclaimed "guru". I want to clean and polish the valve cover gasket. Is there room to remove it without pulling the engine. It would be nice to know before I start unscrewing it. Also, I assume the gasket will be toast upon removal. Best source for a new valve cover gasket is?
Here's a question unrelated to carbs and motor health, hopefully avoiding any further rude remarks by a self proclaimed "guru". I want to clean and polish the valve cover gasket. Is there room to remove it without pulling the engine. It would be nice to know before I start unscrewing it. Also, I assume the gasket will be toast upon removal. Best source for a new valve cover gasket is?
No engine will have to be removed to take the valve cover off. Unless you want to buy a kit that makes the two top frame rails removable. The make a kit that you cut the tubes out, weld in ends on the tubes that make them removable. I think there is a company that makes a bolt in kit but I havent seen it in a long time. It is not terribly difficult to remove the motor but it does require two people because it is heavy. You dont have to remove the valve cover to do valve adjust but if you are wanting to replace a leaky gasket then you will need to remove it, the gaskets can be stuck on there very hard if its never been apart. I strongly suggest doing the compression test before going any farther, would be a waste of time to pull the engine do the valve cover put it back in then find out the motor is shot.
I have used the cheap gaskets from cb750 supply and they do work as long as the surfaces are in good shape. The best gasket in my opinion is the oem honda, they are thicker and conform better to any irregularities in the sealing surface.
I have used the cheap gaskets from cb750 supply and they do work as long as the surfaces are in good shape. The best gasket in my opinion is the oem honda, they are thicker and conform better to any irregularities in the sealing surface.
Pabeye
Older than Dirt
Thanks Dirt.........while on the subject of compression test....the thread on the plug holes is 10mm right? Also can I use one of the compression testers that do not thread in but have a rubber tip on the end and ya just hold it in place. Thanks as always.
