#4 is cutting out on me????

[natemoen]

Ok. So ever since I got this bike (about 2 months ago now) it has not run well. After I got it put together again it has always had a lag between about 1500 and 4500 RPM. A couple of weeks ago I pulled the carbs and cleaned them, cleaned them and then cleaned them a couple of more times for good measure (no I am not joking). I checked the float height (I think I did it right and they are all set between 25.55 and 25.87 mm if I am measuring right). I bench synced the carbs and then synced them when I got them on the bike (it might not be the best sync cause I really and learning as I go here but they are all within about 15 - 18 mmHg with a Carbtune). After all this it still is lagging and bogging down just the same.

As I was syncing I noticed the #4 cylinder was cutting out intermittently. It seemed that it had no patter to how it was cutting out. It also pops randomly and especially on decel. After I synced it I connected the four vac ports (it seems to run smoother that way). I then ran the rpms up to about 7500 and held it there for a bit and then hit the kill switch. #1 plug was a nice dry tan #2 Dry and black #3 dry and black #4 was soaking wet and black. of the four idle screws #4 is already set the leanest of them all at a little less than 1 turn and the rest are at about 1 1/4 or so.

Bike still has the stock airbox with an unknown aftermarket 4-2 exhaust

Compression numbers are #1 150 #2 150 #3 140 #4 140.

Jets are:
Pilot 45
Needle Jet 266
Main 137.5
Air 210

Any help you guys can give would be great! I am getting desperate here!

TIA

[bikerphil]

The thing that sounds strange is the 210 air jet you are running. IIRC, 185 is the correct size.

[Ken Talbot]

Have you tried removing the plug cap for #4, trimming the wire 1/4", and reinstalling?

[natemoen]

I believe you are correct with the 185 for the air jet. The PO had the carbs gone through by some bike shop last fall. he also gave me all the old parts that were removed and those were 210 as well. If it was the air jet though it would be causing problems across the board though and not just #4.

I forgot to mention in my OP that I have also already checked the pickup coil wires and I have done the new wires in old coil fix so I highly doubt it will be the plug wire.

[bikerphil]

Just saying, the larger air jets may be the cause of the lagging and bogging down. I've experienced similar problems with using too large air jets, 190's IIRC. Swap spark plug wires 1+4 and see if the problem follows over to #1. Clean or change that fouled #4 plug too.

[TopCatGr58]

Hey Nate,

No aspersions on your skills, just asking because we can't see the carbs, and aren't familiar with you. Okay, multiple cleanings you say, but were they fully disassembled? Center vac. slide needle jet removed out thru the top of the carb body, etc.!?

Secondly, black plugs not good. Do you know what BRAND of pilot jets they are? Also, there are two styles of pilot jets that can be gotten to fit into the carbs, but one type....the VM is not the right style and can cause excessively rich conditions even with the otherwise correct jet size! Go to www.mikesxs.net and check out the carbs/fuel section, jets, there is a diagram showing the difference between VM and BS style pilot jets.

Also, there should be plugs over the pilot jet tower...large flat head screws. Just making sure that the pilot jet towers in the bowl are not OPEN sucking fuel directly from the bowls instead of thru the main jet tower and sharing tunnel.

The popping on decel is common with all aftermarket pipes, but can be reduced with proper exhaust gaskets, and richening up the pilot jet screws.

Also, that the upper carb body "T" fittings are truly OPEN, they are the bowl vents, and can get crap inside the "T"'s even though the tubing can be clear, and also that the ports on the air box they are plugged into are OPEN and flowing air, can also get clogged causing the carbs to flood!

T.C.

[natemoen]

Phil: I will try swapping plug wires tomorrow.

TC: 1) I removed the diaphragm and needle assembly and checked for cracks and holes in the diaphragm. I could not take the assembly apart because I could not get the snap ring off inside the hole and do not have a long reach snap ring pliers and everything I could think of to use to get them off I could not get it.

2) It was a K & L kit I believe that was put in by the PO. The pilot is the style with a 1 -2 - 1 -2 hole patter which if I remember correctly is the BS style pilot jet.

3) the plugs are still over the pilot jets.

4) the popping is only coming from the right side of the exhaust from what I can tell?

5)When I had the carbs apart I cleaned out the t's and the airbox so the air vent is for sure open.

Thanks so far guys keep the advice coming and I will try and test out any theories that you all have!

[Ken Talbot]

I have done the new wires in old coil fix so I highly doubt it will be the plug wire.

Ah, the plot thickens. Just for a giggle, see if you can swap the leads for #1 and #4. If the problem moves over to #1 you will be one step closer to a solution.

[natemoen]

Ok I switched #1 & #4 plug wires, same things still.

As I said before I connected all the vac ports on the carb intake boots, I have clear tubing running between them all and I now see that the tubing between 3 and 4 is coated in black...something. I cant see between 2 and 3 because the tank is on but the tube from 1 to 2 is still clean and clear.

Something else that I totally forgot about but noticed when I was looking through my notes that I had when I was going through the carb is that the float in carb #4 is different (derr this might just be my problem here). its not the original brass style (like the rest) and its also not the later style plastic floats. Its almost a composite foam or something. I did get the original float from the PO but it is kinda dented and has some solder repairs on it (big huge ugly globs). I am going to sand the solder down and drop it in some boiling water to see if there is still holes in it and I might pull the carbs and put that float in and see what happens.

Any other thoughts from anyone would be great. I will let you know what happens with the float. If anyone has an extra brass float that is good and would be willing to part with it I may be in the market for one soon!

[natemoen]

Ok the old one is totally shot. It had about 8 little holes in it and is not worth it. So what should I do now try and adjust the height of the #4 float to get the levels the same or buy a new (or new to me) float that matches the rest? If I adjust this float which way to I move the float to lower the fuel level (when the carbs are off and tuned upside down) do I lower it or raise it?

[Ken Talbot]

Something else that I totally forgot about but noticed when I was looking through my notes that I had when I was going through the carb is that the float in carb #4 is different (derr this might just be my problem here).

What was the title of that old radio show - "The Rest of The Story"!

Yup, when you consider what a difference 1mm in height makes between floats that are identical. Sounds like you may have a sinker rather than a bobber.

[natemoen]

Ok pulled the carbs out a few times today and just adjusted the float in #4 until things seemed to run good plugs look ok for now I will check them again after its got a few miles on it. So now it idles good sitting I can run up and down nicely through the RPMs.

Now when I am driving it it still has that stumble between 1500 and about 4500. Would that be that 210 air jet???

[bikerphil]

Now when I am driving it it still has that stumble between 1500 and about 4500. Would that be that 210 air jet???

The air jet does control that RPM range IIRC, so there is a good chance those 210's are leaning the mixture out.

[natemoen]

$50 for a single float http://www.motorcyclecarbs.com/FLOAT...10033C2434.cfm Screw that I will suffer with the oddball that I have. Unless i can find a used one somewhere.

Is someone able to confirm that this is the correct style air jet that I need? http://www.motorcyclecarbs.com/MIKUN...0_P2173C13.cfm The manual says that 180 is the correct size, I just want to make sure that this is the right one.

[bikerphil]

Now I'm confused over here. After checking the specs for the 78 carbs, 210 is listed as the correct air jet. Now the 79 carbs specify a 180 air jet. I think we need a carb super guru to chime in on this one.