Walbro WR7-5 ... CCW 340 not running

[Curlymurt]

My 72 project has hit a snag. The darn thing was running from a gas can prior to starting this project this year. For the last 3-4 weeks (since the sled has been back together), I haven't been able to get it started.

So, I naturally assume my great luck with the Walbro has run out. After some carb fiddling, I'm now confused. It doesn't look the same as in the manual. In what order does the needle diaphragm rest from bottom to top? Do I put the diaphragm first and then the gasket? Or do I put the gasket and then the diaphragm? Or do I even need the gasket and should just use the diaphragm between the plates?

One would assume air is getting into the seals around the crank, but I haven't found any evidence of such... Except that I replaced the seals AFTER my gas can run.

[Curlymurt]

Based on a photo of the gasket kit from Parts Reloaded (I think that's where I got the kit from 2 years ago), it looks like they've got the diaphragm and then the gasket on top of that. So, that's what I did.

Also, I noticed when pulling the start handle that gas tries to flow back from the overflow tube... translucent fuel lines for the win. It only occurs when the choke butterfly is restricting airflow. When the choke is open (off), it doesn't backflow from the overflow. In both scenarios, the throttle plate is wide open. I'll study up on some of the diagrams of this carb to find out what's being restricted and try to determine why.

Edit: While I was out running around, I realized the orange umbrella check valve... hmm, check valve... might have something to do with it. So I took the carb apart for the 87th time and cleaned underneath it. But, that didn't work. Long and boring story shorter, I decided to bend the carb needle arm so it would be way too high and undoubtedly hit the diaphragm (or just be stuck open); I had it adjusted per the manual, but because I don't seem to have the same diaphragm as the manual, I threw that recommendation out the window.

Watch out, it spits! Gas was flying right out the front of the air tube on the carb, but it was purring ... eh, gurgling. Once I got my smoke detectors turned off from the smoke (garage door was even open), I decided to air it out a bit before I try to "fine tune" the needle arm. Once it starts that way, then I'll mess with the idle and high speed needles. Snow is supposed to come tonight so hopefully this is close!

[jep_800]

I'm not completely familiar with your model Walbro. But I believe the only thing between the carb body and the metering plate is the metering diaphragm. The center button must be facing the carb body, so that center button can touch the metering arm. As you found out, if you raise that arm too much, you'll get way too much fuel and it starts to spit out of the carb throat. The gasket you show almost looks like the fuel inlet gasket which is the last one to go in the stack, but not sure. I've sent a message to a guy over on Vintagesleds.com who has a thread about rebuilding the Walbros. I've used it a couple times to make sure I got the steps right. However, his photos don't show up anymore so probably a domain issue. I hope he can repost those, as it is very helpful. If so, I'll post the link to it.

Here's a couple shots of my WRA-31 after I got the carb body separated from the stack which shows the metering diaphragm as I found it, and removed.

Jason

[Curlymurt]

Interesting. That's definitely a different diaphragm than I've got. Mine is flat and super flimsy, so maybe I do need the "extra" gasket. What you have is what the manual shows. Maybe I need to try to source one of those.

And, thank you for the photos! That's super helpful to know what I'm supposed to be looking at (even though they are a little different WR series carbs).

I'm struggling to get the machine to idle between the 2200-2600 recommended range. In fact, I can't get it to idle at all as the RPM's drop off and fuel spills out the front hole in the carb. If I leave the throttle plate open just a hair, then I can hold it at 2200-2600... I guess I could always just adjust the throttle cable, but that means my carb still isn't functioning correctly.

[Curlymurt]

I'll have a write up of my findings and solutions once I get a chance, but I have a question:

Does this sound sluggish when going full throttle? Nevermind the shaking camera work... It's 13 degrees.

https://youtu.be/fotcaU4HiWo

[jep_800]

Yes, but I think that's just a tuning issue. It seems to bog down for a bit before wide open. If you're sure all passages are clean, parts are clean, needle and seat are good, and diaphrams & gaskets are new, then you just need to adjust the carb accordingly. Here is an excellent source for maintaining the Walbro Carburetor. It is from Vintagesnow.com

http://vintagesnow.com/Carburetors_file ... enance.pdf

And this one from Foot Flyer: http://www.footflyer.com/fix/motor/carb ... walbro.htm. This one is a basic guide for any Walbro, not specific to snowmobiles, but the steps are identical. I'm trying to find the one I used to have which dealt with adjusting the carb on a snowmobile, but I will tell you the steps are the same.

I think if you followed this, you'll get that bog out of the system. If it doesn't, then you are looking more at an ignition issue which could range from points, to coils, to timing, etc.

Let us know after you do some fine tuning. Good Luck!

Jason

[jep_800]

Here is that other link I was talking about earlier. This was updated by Wankel303 on Vintagesleds.com. This is the tutorial I've used to help with my WRA-31 builds.

By the way, I was wrong in my earlier post. There is a gasket between the metering diaphragm and the carb body. I must not have shown that in my photo, but one does go there.

https://drive.google.com/file/d/1yFonnM ... 2MOIc/view

Jason

[Curlymurt]

That's helpful. I had reviewed some of those docs before, too.

That video was of it running with the diaphragm closest to the throttle body and the gasket on the air side of the diaphragm. But, I went ahead and switched it back to having the gasket on the throttle body side. Which meant pulling the carb off three more times for adjustments.

It runs and doesn't throw gas out the front of the carb, but it seems to run rough and still sounds boggy when goosing it. Due to your tip, I'm guessing its probably points, timing, coils, dirty plugs, so I'll read into some of that. The adjusting the exterior idle/high speed needles didn't seem to help. The engine bay looks like I threw a bottle of oil in it just to watch it splash around... it's an oily mess due a poor exhaust and too much gas flowing for awhile.

[Steven Rempel]

I may have missed it but what fuel mix are you working with. I ask knowing why you are say the engine bay is a mess. I learned that I was getting poor performance from running to rich of a mix. Currently I run 50:1 with strict attention to the mixing using a mineral oil from skidoo.(many other oils work just fine but for me this is what I always have on hand) I have notice that the engine bays are staying much cleaner and they run better with far less fouling of the spark plugs.

it may not help But I have noticed that there is a slight different in the gaskets thicknesses which have caused me a lot of grief in the past when trying to set the needle and fuel pump right, one kit works fine as per the direction and the other neede much less, but I am sure there are other variables playing into that. I love using the choke butterfly as a tool to help set up the needle arm but other times it just been a waste of time for me.

my other question was in that video what is the engine having to work. ie engine no clutch, or everything in place with sled on a stand. if so in what shape is all the rotating parts, from clutches to belts to track to all the rolling bearing. I ask as I have had one sled have a bearing seize and my not knowing spent a ton of time working on the engine only to find out a bad bearing was causing the engine to bog down and have to overcome all the rolling resistants.

these are just my thought and take them for what they are.

[Curlymurt]

Steven,

I'm not sure of the mix but I know it's a thicker mix of oil... the front of the gas tank reads for 20:1, a newly rebuilt engine needing broken in should be 40:1, and 50:1 for normal running (according to the service manual). So, I have no clue what I mixed. It's pretty low on gas so I mixed up a new gallon of 50:1 to try.

I know it's a pain to try multiple things at once, but because it only runs with the carb partially closed, I decided to install a new piece of foam for the intake on my "silencer" to see if that helps also. I was running it up on jacks, but fully assembled, so the belt and track were rotating also. I should be able to get it out tomorrow or Thursday to try the new gas and foam filter.

[Curlymurt]

I took the sled for a 5 minute run in the backyard... It's basically me doing a bunch of figure 8's and annoying the neighbors.

I know you're asking how it ran, so I'll explain. It started on the 4th pull. The gas turned a lighter color, so I know I'm pumping better gas now. There's less popping and spitting, and it does seem a little more responsive, but it's not great. It does think for a half second before jumping when I give it throttle.

Overall, it felt better, sounded better, and idled well. The gas mix helped, undoubtedly. I do still have to leave the choke 3/4 closed, so I'm thinking I'm going to have to go back in and adjust the needle again. I think I saw another thread that talked about which direction to adjust it, so I'll check that out.

Actually, what if I left it how it is? Would I run to lean in wot?



Side note: These sleds are so much more fun than the new models that are heavy and sit high. I love skidding around corners on this thing.