Topic: Is it possible for my bike to be running on just 2 cylinders?

[RainCityRider]

After running for a while not all of the exhaust pipes are hot. 1 & 4 are smoking hot but 2 & 3 are just really warm. I have been trying to adjust the timing and put my timing light on 3 and it worked. So if there is power to the wire what could it be?

[flybox1]

Do the 2/3 cyls kick in if you get the RPM over 4000?

[flybox1]

Air/Fuel/Spark
Its gotta have all three and in the right proportions.
Air - pods?
Fuel - when did you last open the carbs for a clean and a check?
Spark - are 2&3 plugs sparking if the plug is held to the head?  Plug cap resistance check ok?

[RainCityRider]

Air box w/ new filter.
Have a rebuild kit on the way. So, not for a while.
Gonna try one of those test lights in a little bit.

But I rode it to and from work yesterday and to work today. Power feels great! Would it run on just 2 cylinders? Just weird how hot 1 & 4 are when 2&3 were not even close. Water beaded on 3.

Sorry for the stupid question!

[ekpent]

 If the water beaded and did not sizzle that cylinder is not working. Could be a carb or ignition problem or a fouled plug.

[flybox1]

yes, it would run, but it would sound like isht.
dont use aftermarket jets.  you're only asking for trouble.  clean and reuse what is in there.
One of the easiest things you can do with the PD carbs is a clear tube test of the bowl fuel levels.


Also, pull your plugs and look at the deposits on the insulators. (post a picture of them for us to see)
Anything darker than brown, and you have excess fuel or oil during combustion.

[Tugboat]

I rode my 750 from my ex's to my house on just one cylinder - seriously!

[Scott S]

 2/3 are fired from the same coil. Check the points, condenser and coil for 2/3.

[ekpent]

 Ride for a long distance without a cylinder or more firing you may want to take a whiff of your oil for gas. Also pretty hard on the piston and rings with the fuel wash 

[RainCityRider]

I cleaned the plugs on Sunday with a brass brush. And installed a Pemco ignition. I have the coils still to install.
I am getting spark on 2 & 3. Must be a carb issue. I will rebuild and see how that goes.
I will park it when I get home and until I can sort this out.

[RainCityRider]

yes, it would run, but it would sound like isht.
dont use aftermarket jets.  you're only asking for trouble.  clean and reuse what is in there.
One of the easiest things you can do with the PD carbs is a clear tube test of the bowl fuel levels.


Also, pull your plugs and look at the deposits on the insulators. (post a picture of them for us to see)
Anything darker than brown, and you have excess fuel or oil during combustion.

What in this kit should I use?

Carb Rebuild Kit
 Contains: Float Bowl Gasket, Carb Top Gasket, D313 Slide Needle, Main Jet (#105, Stock type for 1977-78F models), Main Jet #110, Stock type for 1978K model), Float Needle, Air Spring, Air Screw Plug, E-Clip, Air Fuel Screw (1978F Type), Air Fuel Screw (1977-78K Type), Needle Jet, Metal Washer, 6 O-Rings. - Made in Japan -

Fits: Honda CB750K (1978),
CB750F (1977-78) Supersport

Note: Each Kit Rebuilds One Carb, Order the Quantity of Kits you Require
Part #: 48-1737

[ekpent]

When troubleshooting best to use new plugs. Brass brush may not do much for a fouled plug. As for the aftermarket rebuild kit I bet someone says the gasket. 

[Scott S]

 Use the gasket, O-rings and float needle....re-use your stock brass. After a thorough cleaning, of course. And do us a favor: Write down the jet sizes and clip position while you're in there.

[thirsty 1]

2/3 are fired from the same coil. Check the points, condenser and coil for 2/3.

This. ^^^^

[RainCityRider]

2/3 are fired from the same coil. Check the points, condenser and coil for 2/3.

This. ^^^^

No points. just installed pamco.

[RainCityRider]

So after some fiddling #3 started firing. But #2 still "Colder than a well diggers aZZ" 

I was pulling #2 out and the wire pulled off the plug, I thought Yowza I found it! So I trimmed the wire and screwed it back on.  Still cold. Gonna get the new coils I have at home installed and go from there. And get new plugs.

Thanks for the help on the carb parts too. I will check in and give y'all progress reports. And I will write down the jet sizes when I get in there.

Cheers & Beers!

[RainCityRider]

Got the coils installed and put new plugs in. It runs , But 2 & 3 are still running cooler. Gonna wait for the carb kits and give that a go.

Old plugs #2 was defiantly fouled. but now 2&3 are coolish again.

Timing it weird too.

If I set at "F" on idle the advance is really high. If I set to advance, idle is closer to the "1-4" than it is "F". Could this be from carbs too?

[Scott S]

 You have it advanced, it sounds like. Don't worry too much about the marks at idle. Set it between the blue and green marks as seen in the attached pics at full advance.....about 2500-3000 rpm.

[Scott S]

 At idle, it should be closer to the yellow mark, but don't worry too much about getting it exact at idle. Set it for full advance. That's where your bike will spend 98% of it's time.

[flybox1]

Gonna wait for the carb kits and give that a go.

What part(s) in a carb 'kit' is going to make your bike run better?   

[RainCityRider]

So, I removed the carb last night and took the float bowls off. They were pretty caked in the bottom. I cleaned it out with a dental pick and dumped them in a bowl (pic #1 yuck!). I started taking the engine side bracket off but then thought better of it and put it back on. I removed the throttle diaphragm, it was bent. I loosened all the main jets, for kicks, then put them back in by hand. Sprayed some WD40 through the jets, I was out carb cleaner and the stores were closed. The main jets seem ok maybe a little low flow. But all of the slow jets seemed clogged.

I got a bunch of parts today.  I got a new pump diaphragm, new floats, carb kits with o rings & jets, air box boots ( all mine like to work their way off the carb), and new Iridium plugs (I know the jury is out on these but I will try them and can get regular ones if needed) .

Q's
1) Do I need to take the whole thing apart or is this overkill?
2) If so where do i find the proper manual, step by step directions, or better yet a video on doing it? maybe I will make a video. I do have 3 carbs to rebuild.
3) Should I try the jets I got, order new Keihin jets, or reuse the old ones? https://www.jetsrus.com/a_jets_by_carburetor_type/a_jet_kits_keihin_selection.htm
4) I got a cleaning tool with the kit. But should I get a jet drill too?

I will get deeper into them tonight.

Thanks for all the help guys!

[Gene]

Sharper minds than mine will chime in - but, imo - re-use your existing jets, just clean them up well. Unless you got Keihin brass in your rebuild kit those parts are useless to you.  use the O-rings. NO JET DRILL. And you may not want to trust the cleaning tool either - just don't damage the brass, it's a very soft metal.

Whether you need to split the rack or not - I dunno, never done it.  Depends on how crappy everything is I suppose and how much cleaning is necessary, I can't answer that.

Rather than thinking of this as a rebuild, think of it as a thorough cleaning.  And, you may want to consider boxing up your carbs and sending them to member harisuluv for rebuilding/cleaning/synching.

Good luck with the project.

[Scott S]

Throttle diaphragm? Whatchoo talking about, Willis?

[RainCityRider]

Sorry Carb pump diaphragm. I have seen it called both.

[RainCityRider]

^^^^^^^^^^^^^^^^^^^^^^^^^^^

Sorry Carb pump diaphragm. I have seen it called both.