1978 Rat Bobber - Pics and Video - Finished (but needs tweaking!)

[SpongeBobbed]

Hey Guys,

I put together a quick build thread on this bike previously but I've been having a couple issues lately so I thought I would reach out and see if anyone can point me in the right direction.
Finally got my bike together after a few years of late nights in the garage, and I'm happy to get this thing on the road.

Been having a few issues getting it to run right, and it seems like every time I fix one issue, another one pops up. I was having some charging system issues and it turned out my rotor was fried, so I put in Hugh's PMA (awesome). Now my bike is charging like a champ but the carbs are acting up. They were working great before but now they are being a bit sporadic.

I highlight it in the video but here's the overview:
- 1980 bs34 carbs with 137.5 mains, stock idle jets, and the Canadian needles.
- Jet Needle currently on 4th slot.

When I hit about 2000 rpm it starts to bog a bit. I can't tell if it's lean or if it's rich but it sounds more rich to me. It makes a "papapapa" sound and then once I hit about 3500 it goes away. I think if it was lean it would just cut right out and then come back at 3500. I am wrong there?

Also, it doesn't want to go back down to 1200rpm when it's resting at a light. It likes to stay at about 3000. I know that is a tell tale sign of a air leak but I can't seem to find it anywhere. I've honestly spent about 20+ hours trying to get these carbs tuned. Taking them off, switching jets, putting them back on, etc. Getting frustrating.

If anyone has any advice please let me know. I'd really appreciate it!! Cheers!

 

[TwoManyXS1Bs]

Haha, so if anybody asks, YES, you're running 2 fenders!

Could try the slide diaphram leak-down test.
And, see if the inner flanges of those air filters are blocking the diaphram ports and air bleeds...

 

[deadchef]

hi sponge,
i run bs34's with canadian needles. here is what i run and it works well for me and has for a few thousand miles so far. spark plugs read well too.

bs34
47.5p
137.5m
canuck needles at #2 slot
uni's
free flowing exhaust

really with jetting though you have to do some work. you need to try several and once you think you got it try the next one up and next one down. and of course, you need to first make sure that the carbs are in good working order (all passages clean, seals/oring good, floats adjusted and working, etc)

good luck!

 

[SpongeBobbed]

Haha, so if anybody asks, YES, you're running 2 fenders!

Could try the slide diaphram leak-down test.
And, see if the inner flanges of those air filters are blocking the diaphram ports and air bleeds...

Thanks TwoMany, I'll check the diaphrams using that test and see what comes up!! Never thought about the filters so I'll check that out as well.
Cheers!

 

[SpongeBobbed]

hi sponge,
i run bs34's with canadian needles. here is what i run and it works well for me and has for a few thousand miles so far. spark plugs read well too.

bs34
47.5p
137.5m
canuck needles at #2 slot
uni's
free flowing exhaust

really with jetting though you have to do some work. you need to try several and once you think you got it try the next one up and next one down. and of course, you need to first make sure that the carbs are in good working order (all passages clean, seals/oring good, floats adjusted and working, etc)

good luck!

deadchef, thanks for the details on your carbs. I'm going to set mine up the same and see if that helps. Sounds like a similar set up so it at least gives me a good place to start. I'm going to do a thorough cleaning of the carbs today and make sure everything is set up right. I'm reluctant to change the pilot jets though because they seem to be stuck and I'm worried about breaking them off. I tried heating them up with a soldering gun but no luck yet.

 

[SpongeBobbed]

Also, here's a video of me starting the bike to give you an idea of what it currently sounds like.

Getting some pretty good backfire on deceleration.
Thanks!

 

[ippytattoo]

It sounds to me like you are lean in your pilot circuit, the left pilot circuit may be partially plugged and you may be rich in your needle circuit. Did you get the Canadian needle jets when you got the Canadian needles? They have to be used together.

 

[slawbait]

this bike rules hard, i really dig the fender light shroud

 

[SpongeBobbed]

It sounds to me like you are lean in your pilot circuit, the left pilot circuit may be partially plugged and you may be rich in your needle circuit. Did you get the Canadian needle jets when you got the Canadian needles? They have to be used together.

Ippy, I agree on the leanness in the pilot. I spent all afternoon searching the city for pilots but no one has them. Looks like I'll have to wait a few days before they arrive. In the mean time I have the same carbs on my cafe (with the 45 pilots) so I'm gonna take those out and put them in these carbs to see if that clears anything up.

I did use the Canadian needle jets as well. So that's not the issue. I'll keep messing around and hopefully I can figure it out!!

 

[SpongeBobbed]

this bike rules hard, i really dig the fender light shroud

Thanks man! People either love it or hate it but I like it! Looks a bit different and holds everything nice and snug while giving me a place to mount my speedo and switches.

 

[Dustinj]

I dig it man. I'm using a front fender for the rear also. Would you post up a pick of how you mounted it. That's exactly how I want mine.