Help Find A Cure for Crazcnuk's bike?

[egsols]

Craz,

I would assume that your needles are going all the way up due to you being able to reach redline up to third. I can't remember what you said about your float adjustment. My brain is starting to hurt. You bike seems to run fine, the mileage you are getting is comparable to mine.

The only thing I can think of right know is that you must not be getting enough fuel under max load. Options for this could include, float adjustment, clogged float valve screens, kinked..clogged fuel lines, clogged/small/backward in line filters, clogged tank towers, clogged/obstructed petcocks, clogged tank vent, clogged float bowl vent. I know you've probably checked all of these but I needed to add my 2 cents.

[Poprock]

Visiting with an XSive who has a new 1200 kit in his SG. He had OK performance but was disappointed in the throttle response. Everything looked good, carbs all tuned to perfection. Then he replaced the vacuum seals on the intake boots. He got more power quicker, arm-pulling thrust from the throttle, improved mileage, etc. The vac leak was slowing his spark curve, failing to raise the slides sufficiently, starving him for fuel at higher rpm. Put new caps on those synch taps and see if it helps.

[Crazcnuk]

Went on a 650km trip thursday friday.

I lowered my floats 1mm to see if I could get rid of the low end bog. It helped a little, but still had no jump off the line.

I got 43mpg (imp) going to Edmonton, and 36mpg on the way back, against a stiff headwind.

I used a little over a liter of oil.

Derwat hit 46mpg (imp) on the way in and 42mpg on the way out. He hit reserve at about 190kms on the return trip.

I got to thinking about the low end bog. When I drop my needles one notch, the bog is gone. Many people, here, have been dropping the float levels, with good results. I am wondering if the reason for this is that we are compensating for needle/valve wear when dropping the floats?

Both should do the same thing (degree?). If we are getting wear in the needle/valve assy. This simply allows more fuel through. By dropping the float level we reduce the amount of fuel going through.

I just remember a topic about whether the floats aren't 'floating' as well after 30 years, but I think that the needles/valves may be wearing and people found lowering the fuel level helped.

Mikuni tuners say that the 34, 38 and 40mm versions can show needle wear in as little as 5000 miles.

Also, there was a question as to why our emulsion tubes have that 'collar' at the top. I am of the opinion it is there to keep the airflow, through the carb throat, from pushing the needle against the back of the tube, to reduce the wear. Since 90% of the time the slides are quite low that guard would keep the wind off the needles most of the time.

[skids]

I think that the collar elevates the liquid above the throat and helps atomize the fuel with the air. You know, less dribble.

[olebiker]

Originally posted by skids
You know, less dribble.

I am workin on it but I didn't know it was common knowledge.

[pete_s]

Carbs sound like they are good

Except I'm thinking the diaphrams are getting hard. Someone may have dunked the carbs in solvent and made the neoprene start to age.
On a assembled carb---

Test the slides by raising them with your finger, they should go up smooth with just the spring pressure pushing down. When you release them they should drop fast - less than 1/2 second to fall. Could be at WOT your butterflys are all open but your slides are all over the place.

Same with your Vacuum Advance, if you suck on the hose it should move the pickup plate smooth and even unless the diaphram is hard it will be jerky. This will afect your MPG just like when the mechanical advance is sticking or broken. I don't know what total advance is but it should be less than 32 deg, you could set up a degree wheel on the crank to check it with a strobe

Things to drive you more crazy

[Crazcnuk]

I've checked the slide operation. They are smooth, and drop quickly with no vacuum. If I lift the slides up, and block the vacuum port, they will, essentially, stay up, until I release the port. They are coming down, but VERY slowly.

I've also tested the operation of both the advance mechanisms. They seem to be working properly.

I am kind of stuck, as to what to try next. Since the fuel economy is up to acceptable now, I am trying to work on the lack of power at the top end.

I am going to put the floats back to stock height (23mm) and drop the needles one notch as that is where I got the best economy, and no bottom end issues.

The only problem is that when I had the needles dropped the last time, although the bottom end problems were gone and economy was the best I had achieved, top end power got worse.

This leads me to believe that my carbs are rich at low-mid but lean at the high end. However, I have gone up to 120 mains with no appreciable difference in top end performance.

I am tempted to drop the needles AND the float level 2mm, then put the 115 mains back in.

Keep in mind that I have worn out a rear tire just trying to get it to run right!. The bike is reliable, and runs fine in all legally acceptable speed ranges, except for bottom end bog, which I can get rid of at will. But nothing I have done has made any difference in the top end.

When I first got it on the road, it would pull right to redline in all 5 gears, but it got 17-25mpg. Now I get 38-42mpg, with no top end power.

[TopCatGr58]

Hey Craz,

Have you tried the larger jets NOW that you have the MikesXS coils on there?? Perhaps it may have been partly a problem with lesser ignition power so it couldn't use the extra fuel as well??

Did you see MadMax's post about his Maxim needing a considerable main jet boost to get it to run right at the higher rpms/power range?? He has Indy filters and 4-1 pipes.

I also have Indy filters and 4-1 pipes, and are running 117.5's, but could easily go up to 120's with the 81 series carbs, possibly even more according to the Dyno I did a few years ago.
T.C.

[pete_s]

Seems you have covered everything, I run with the needle centered and get 45 MPG so I guess you could say I take it easy and my bike is a stock 78 except for the 750 rear end.

The CV tuning guide says that the Main jet is the first step to carb set up so you may be on to something but it's a lot of work to put the parts in and then find it's no better or worse than before

[Crazcnuk]

I had the 115s in with the new coils. However, I still had the larger 45 pilot jets too.

Even with 120s, at full throttle in 5th, the plugs stayed perfectly clean. With the 120's and 45 pilots, the bike loaded up badly at anything under 4000rpm.

Right now I have stock pipes, stock airbox and a K&N element, with the Mike's coils.

[petejw]

hey Craz,
did u clean off any lube
that u put on the slides?
stil note that u state the slides drop slowly,
if they drop slowly there probably rising slowly as well.
other than that uve seem to have done every thing else.

[Crazcnuk]

There is no lube on the slides.

They drop slowly when the vacuum port is blocked. Quickly if the port is open.

[mro]

I am going to put the floats back to stock height (23mm) and drop the needles one notch as that is where I got the best economy, and no bottom end issues.

80+ plus carbs floats are set to 23mm, but I've never seen 80+ carbs with adjustable needles.
I have not read thru this thread. Did you change em?

Float height will affect all rpm ranges, but the needles will only come into play under acceleration and higher rpm.
How did you adjust the pilot screws?

When I was playing with different float heights on a stock 80G I found that going to "low" on the floats caused a loss of power at higher rpm. but still idled and ran OK just crusing. I had set them to 22mm.


mro

[Crazcnuk]

According to MikesXS 1980 Canadian models have adjustable needles. However, the needles in mine don't match the numbers in the manual.

There is a whole discussion on this earlier in the thread.

I found, when I dropped the needles one notch, the bike ran better in the low to mid ranges, but I lost even more top end. The power cut out about a 1000rpm earlier than 'normal'.

If the needles are worn, there will be more space around them at all ranges. dropping the needles puts the wider portion depper into the needle valve, and would effectively counter minor wear in the two.

I have my floats set at 24mm right now, and I have to rev the bike to 3000+ to get it moving. If I raise the floats to 23 and drop the needles, this problem goes away, but I lose top end.

[dbeardslee]

Craz - Somebody had another post up on carbs, and they mentioned Carb Kit Capital . They have some really nice lookin' rebuild kits that include new needles for $15 ea. Next time I do Betsy's I'm gonna try one of their kits. I know you just bought new needles, but I thought I'd pass it along.