Won't idle or run without major throttle

[Guss80special]

Hi. Looking for some advice for my 1980 special. I road my bike yesterday after 2 weeks away. started fine and idled great with no choke. 10 min into the ride it stalled. I could only get it going by keeping the throttle up high. Lots of minor back fires. Barely got it home by feathering the clutch a lot and lots of throttle.

Only thing i changed in the last 2 weeks was to install a non vacuume petcock. Fuel delivery seems fine, and I have tight bung caps on both manifolds now that the vacuum line was removed from left side.

Plugs look different now though. They are usually blackish. They actually looked better. Now. Almost tan. But now the bike doednt run properly. It does start on full choke, but dies again with choke off. I tried with air filters removed, gas cap open. No diff. Battery showing 12.34. Do you think maybe the Tci or coils?

I'm considering putting my old petcock back on?

Any advice is greatly appreciated. G

 

[retiredgentleman]

Engine dies when choke turned off, means your pilot circuit is not supplying enough fuel. I suggest you remove the carbs and remove each pilot jet to confirm they are clear. It has nothing to do with your petcocks. Does your gas tank have rust or debris particles in it?

Your plugs should always be a tan colour.

 

[xjwmx]

Does the replacement petcock have a built-in filter? Do you have a filter in the line? https://shop.advanceautoparts.com/p/driveworks-fuel-filter-lawn-mower-dw-761/6180361-P

 

[Griz]

Double check the fuel delivery. I'm with retiredG. If it only runs with the choke on then it's not getting enough gas?Or freshen up the tank? Here's what gets me. (Doesn't take much) The plugs. so maybe you were running rich all along, now that you have gotten rid of the vacuum your ratios are off? Which would come back to the carbs, and the jets I guess. Did you try adjusting the carbs at all?

 

[Guss80special]

I did take the carbs apart to look. Seemed clean. But I will do it again.
Yes, the new pc has small little white filters.
Every piece of the carb internals were replaced in the last 3 months except the needle. That was to be my next troubleshooting effort as I was missing mid range throttle. Now this though.

Thanks guys. I'll rip the carbs apart and clean well and try new gas

 

[retiredgentleman]

Its not the general carb interior that you need to check, its the pilot jets. You must remove the 2 pilot jets and carefully look with a bright light to confirm the very small orifice is completely clear. If the petcocks have those cheap little white filters that slide on over the brass stand pipes, they are useless. Those little filters will vibrate off the stand pipes and you will find them laying in the bottom of the tank.

You haven't replied about the interior tank cleanliness. Does it have rust or not? When you changed the petcocks, you may have stirred up some debris in the bottom of the tank, which has now made its way into the pilot circuit. Its best to have in line fuel filters between the tank and the carbs. The 90 degree ones that are sold by www.650central.com have worked very well for me for many years.

Are you sure you have replaced the pilot jets a few months ago? If you have never removed pilot jets, you must find a screw driver with a blade tip that is an exact fit into the pilot jet slot. You might have to find one with a slightly larger tip, and grind or file it for an exact fit. If you don't do this you may damage the slot, and then you will be in a mess for sure.

 

[xjwmx]

Yes, the new pc has small little white filters.

I Ihink I've read of those deteriorating and coming off pretty quickly. I turned my vacuum petcock into sort of a manual petcock - just gut it and put gasket paper between the two halves. That gives you run and reserve. Then put a lawnmower valve in the line to give an off. I think you can get fancy bronze on/off valves. Added benefit is you can take it loose at the valve to fill a camping stove

 

[xjwmx]

You might have to find one with a slightly larger tip, and grind or file it for an exact fit. If you don't do this you may damage the slot, and then you will be in a mess for sure.

3/16" bit about 3" long will fit the groove. Sides of all flat bits are usually parallel at the tip unlike regular screwdrivers. Very important. Can often find them in hardware stores in little bins near the register. Colored S2 bit I got at HF is very good but current version might be too short.

 

[Guss80special]

My tank is clean and no rust. But ya, maybe I knocked some stuff around while installing the pc. I do have an in line fuel filter.

Yes. I did replace the pilot jets a couple months ago. That was the best cure for my initial good idle, but no throttle problem. Now it's no idle lol. I'll take them out tonight and look and clean. Yup. I have a good driver that fits that little pilot jet nicely. Thanks!

 

[Guss80special]

Took the carb apart and removed everything. Gave everything a cleaning with carb cleaner. Not the idle screws, slides or float valves of course. Nothing rubber. The pilot jets looked fine but it did take a few sprays of cleaner before I saw fluid spraying out the tiny hole so maybe they were clogged. Had to force the bike to start with choke and drove it around the block 5 times. Turned choke off as soon as I pulled away of course and it seems better. I stopped a few times, no stall. Turned it off and waited a min. turned back on and it idles ok again. So I'm hoping this was a one off clogged pilot issue as you all thought thanks for the help. See photos of the pilot holes for fun. Plugs were black and carby again.

I also took the pc off. The little filters were still on but only barely. Useless I must say.

Now I'm back to my original problem of not getting smooth throttle through all Rpms. Also have no power at full throttle. I got some advice from another thread to start looking at the needle settings.

While I had the slides out, I un screwed the needle setup and noted that the clip was in the 3rd notch from the top. Another thread advised me to start experimenting with needle positions. So I'll try that next weekend I suppose.

Thanks for the help guys. I appreciate it

 

[Guss80special]

With and without flash. Tough to see in there

 

[fredintoon]

I Ihink I've read of those deteriorating and coming off pretty quickly. I turned my vacuum petcock into sort of a manual petcock - just gut it and put gasket paper between the two halves. That gives you run and reserve. Then put a lawnmower valve in the line to give an off. I think you can get fancy bronze on/off valves. Added benefit is you can take it loose at the valve to fill a camping stove
View attachment 107372

Hi xjwmx,
too cheap to buy Coleman gas, eh?
Turning the petcock's lever to point straight up turns the fuel off.
Your photo plainly shows the little nubbin you need to file off the petcock's faceplate so the lever can point straight up
so long as you file it a tad shorter so it clears the tank.

 

[xjwmx]

Now take a can of carb cleaner and put the hose in the hole the pilot jet came out of, all the way past where the jet seats, to the bottom. Put your index finger over the group of holes behind the pilot hole and your middle finger over the air jet for the pilot circuit in back of the carb, and squirt. An intense stream should shoot out of the pilot hole. A trickle isn;t good enough. People on other sites like B-12 Chemtool carb cleaner. It's pretty common.

 

[xjwmx]

Hi xjwmx,
too cheap to buy Coleman gas, eh?
Turning the petcock's lever to point straight up turns the fuel off.
Your photo plainly shows the little nubbin you need to file off the petcock's faceplate so the lever can point straight up
so long as you file it a tad shorter so it clears the tank.

LOL. Guilty of you name it. I figure with a Coleman generator being about $7 on ebay I can run a lot of gas through it and still be money ahead. Last time I noticed Coleman fuel was like twelve bucks a gallon or more Very cost-effective. Ran gas trough it almost every day for a year before it became big yellow flames and needed a new generator. Scared my neighbor in the man camp in ND and he ran over thinking my trailer was on fire -- nah, just making coffee

 

[5twins]

I see from your other thread that you replaced your mains with #145's? Those might be too big and could be part of the cause of your rich and rough running. A 137.5 or 140 is probably more appropriate. Yes, you probably need to lean your needle settings a step (to slot #2 from the top), especially with those big mains. What you have to understand is the 3 circuits in your carb overlap slightly. Changing one affects part of the one next to it. In the case of larger mains, they bleed over into the upper midrange and make it richer too. This often requires a needle adjustment (one step leaner) to correct.

You spend most of your riding time running in the midrange circuit so it has a big influence on plug color. So, start by leaning your needles a step. That should improve your plug color. If the bike still won't take full throttle try reducing the main jet size.

 

[Guss80special]

Ok. Thanks for the cleaning tip!!!

Correct. I put in a 145 main and a 45 pilot as per xsdirect recommendation range of (142.5 - 147.5) main - I split the diff and got a 145. They also recommend air jet of 127.5 but they don't seem to sell air jets, so I did not change those. I do have the original main and pilots but I have no idea what size they are. Xsdirect has lots of different sizes so I'll order some smaller ones as you suggest, but start at the needle setting first

In the topic of jets... should I try and find mikuni originals?

My pipes are loud so that doesn't help a rich situation.

Thanks for the great explanation. I'm determined to get this bike purring as best I can. I'm getting good at taking the carbs off and on that's for sure.

 

[motormike]

... gas cap vent..?....

 

[5twins]

Yes, original Mikuni jets are best and really don't cost much, if any, more than the repops Mikes/XSDirect sell. The jets used in these are nothing special, just common Mikuni jet types. If you have any local shops around that cater to dirt bikes and/or snowmobiles, they probably sell them. Here's the main type you need. Also, the small round type is what is used as your air jet .....

Be aware that if you reduce your air jet size, you will be reducing the amount of air being fed to your pilot/idle circuit. This will make it richer and you may not need to do that since you have already done so with the larger pilot jet size.

 

[Guss80special]

Great info 5twins... thank you

What do you mean by "gas cap vent"? I've opened the cap and gave it throttle and does not seem to change anything.

 

[motormike]

..ok.. my buddies 81' Special had the same issues... we kill'd off many grey matter cells we'll need in our golden years before we discovered a clog'd vent on the cap...