Ikea 1984 XJ1100... some assembly required

Hello everyone,

It's been a while, I got called away from home for work and have just got back this week, so here's a few things in an update. The bike passed inspection without any issues, Wahoo!

I took it on it's first ride and it was fine, maybe a little weak on the acceleration. However after 100 kms I had to flip to the reserve. I filled up and did the math, it's using 19 liters per 100 km. That's 1980's Chev pick-up truck hauling a trailer kinda fuel consumption. Something is seriously wrong! I confirmed the gas isn't pouring out onto the floor so it's going into the carbs. I didn't think it would be possible to jam that much gas into an 1100 but here we are. Going up to post #73 I moved the needles to allow for more fuel, I didn't expect this much fuel! So today the carbs came out again. I can remove the needles with the carbs in the bike but I wanted to be double certain the float heights are good. So back on the bench. I set up my standard level check mess.

I have confirmed all 4 are on spec, here's some pics. With that done I moved the needles back and after re-assembly I'm back to stalling off idle. To say the least I'm not happy with this. There aren't too many thing I can adjust that affect fueling. With the float levels good and the needles set that kind of about it, without changing jets. The only other thing that I can think of that adds fuel is the enrichment/choke circuit. Has anyone seen these go bad and dump in the fuel?

I'm going to change the oil and filter as fuel must be washing down past the rings.

I'd welcome some suggestions if you guys have them.

 

Some ideas here from bad emulsion tubes to no ignition advance, the latter would make it really lack power

https://xjbikes.com/forums/threads/1982-xj1100-maxim-gas-mileage-is-horrible.127126/

If mine I would need to test again just to be sure it was really that bad - 12 mpg

 

Hey Rooster,

Thanks for the quick reply! I'll check timing tomorrow!

 

Are you sure the progression holes are all clear?
Are your idle/primary jets correct/not eBay replacements?
Slow throttle opening pulls fuel from the idle jet and progression holes, wanging the throttle open pulls fuel from the emulsion tube/needle, this involves the slides, springs and the hole under the slide (ignoring air jet correction for now)

 

Rooster and Minimulty,

I am week behind on posting so here goes. Last weekend I moved the needles into the middle position again and fiddled with the idle mix screw until I got satisfactory off idle performance when the engine is warm. We redid the 100 km trip, (this time foe a cold soda not lunch) and returned. With 100 km on the odometer I used 12 L of fuel, Better! That is about 22 MPG for those who think in imperial measurements. This is still pretty low for one of these things with what you guys have been saying. On Friday I moved the needles again up one more notch and again added a bunch more adjustment to the idle mix until I again get reasonable off idle (1500-3000) performance. We were about to go out one more time for the 100 km soda run but it's starting to rain, so if things dry out this afternoon I'll get another data point. I'll keep you posted.

Mini, I am using the stock jets and internals that came with the carbs and I ran through all the jets and progression hole with a tag wire, tiny little brush or welding tip cleaner tool where appropriate, everything had a 24 hr dip in the carb solvent bucket and a good thorough scrubbing and finally a dip in the ultrasonic cleaner after that. all the internals are as clean as I know how to make them, good call because i got a bunch more the second time I went through the carbs a few months back. I'm happy with the level of clean.

 

Still behind a week,

Last Saturday I moved the needles 1 step leaner and fiddled the idle mix until it felt like the off idle was ok. I went for a test ride and absolutely nope! under any load there was no of idle, it just stalled out. The needles aren't the answer.

So This week I pulled the carbs, brought the needles back to center and started disassembly. I confirmed I've got 112.5 jets for the 2 that are still legible and that it's clean. I found a little crud in the bowl that I think is from the crappily DIY tank liner job that previous owner did. but I think I found the problem. I am a dumbass.




I made the critical error of re-assembling the carbs the way they came apart, without double checking they were correct when I got them.

1) I know previous owner said he cleaned them. (not clean).
2) I know everything previous owner did was wrong and needed correcting.

These two facts = me being a dumbass.

Which way are those floats installed? Looks a little different than the service manual picture doesn't it?

Will one of you fine gentleman confirm the damn floats are in upside down so I can fix them and be clear of any doubts?

This would certainly explain the insanely bad fuel use and feeling sluggish. I'm actually surprised it runs as well as it does.

 

I forgot to mention, I pulled the side cover and broke out the timing light, the ignition is advancing.

 

I think they are correct, but an easy way to tell is does the "stop" tang sit against the post as it should to set the fall of the floats with no fuel. You can see it here on page 18.

https://www.xj4ever.com/mikuni carb cleaning.pdf

Did you do a good inspect on the emulsion tubes to see if the should be round hole is oval?

 

The floats are upside down, the point ends should be facing the bowls. He has the point ends facing the carb bodies. The floats will be too low. Fix that and do a wet set of the floats refit carbs and synch, making sure your valve clearances are spot on before you sync the carbs.

 

This used to be a common issue on later carbureted minis, with the spring loaded needles. It wore the jet oval, which needed a height adjustment of the jet. This would sort the idle (SU carbs have only the main jet), problem being then the mixture of idle was weak - instant flat spot. Change to new jet - problem solved.
On the XJs the main jet is on the bottom, but in reality the top of the emulsion tube and needle has a massive off idle effect, the tube needs to be carefully inspected.

 

Thanks guys,

I gave it a try on one carb and bent the needle tang and installed with the float the other way around, the bowl will not fit at all. Even with needle removed the metal part of the float binds on the housing preventing the bowl from fitting. Despite the illustration in the shop manual the float has to go in the way it is. I think at this point I am committed to another complete tear-down and close inspection. I'll give it a look tomorrow.

 

I'm actually caught up on my posting. This weekend was carb weekend, I declared war and went to battle. The carbs came apart and got fully disassembled. The bodies and bowls went for a swim in my big ultrasound, with a pine-sol and water mix for a good hour each. I ran the passages again with wire and brushes, rinsed and blasted out with compressed air. The innards got a dip in the small ultrasound, first in carb cleaner, then after a rinse in vinegar. They are bloody clean. Since clean beyond clean is the common theme on every post about these carbs so I went a little overboard, I dumped the glass beads from my blast cabinet and after a cleaning added baking soda. I then gave all the brass a blasting and then another rinse and the final dip in the ultra sound with more compressed air, and passage verification. If these aren't the cleanest 41 year old BS 34 carbs on the east coast I'm done and going to buy a Honda, with fuel injection. I finished up for the day after re-assembly and ganging the carbs back together, I'll verify float levels again before they go back. Then it's time to check the balance again before trying them out.

I decided to change out the plungers for the choke circuit, the spares have been soaking in a wintergeen/rubbing alcohol mix that the old jeep guys swear softens up old rubber seals. I still think that could be a possible source of the extra fuel. Hopefully they seal better.



the first two pics are post cleaning in the ultrasounds. Pics three and four are a comparison before and after soda blasting.

 

I did a quick look thru the thread and couldn't find any info on the jets and needles, here is what they are supposed to be:

Years & Models: 1982-84 XJ1100 models
Carb Manufacturer: Mikuni
Carb Series: BS34
Carb Model ID: 10M00
Main FUEL Jet Size: #112.5
Pilot FUEL Jet Size: #47.5
Main AIR Jet Size: #140 (non-removable, in carb throat)
Pilot AIR Jet Size: #170
AIR COMPENSATOR Jet Size: not used
Starter FUEL Jet Size: #25 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #5GLZ-33 (4-position, adjustable height) or 5GLZ-34 (single-position, non-adjustable height)
Main needle JET Size: #X-2 (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 5.0mm +/- 1mm (.197" +/- .039")
Idle RPM's: 1,100 rpms
Vacuum at idle: not specified
Vacuum, allowable difference between cylinders, at idle: below 10mm Hg (below 0.394" Hg or below 10 kPa)


The one picture of the main fuel jets shows the 112.5 size on one, can't read the other.

You should verify that all of the other "marked" components (jet needles, pilot fuel, pilot air, emulsion tubes) are the correct sizes.

Also, be aware that with an unknown history, there is the chance that the BS34 carbs aren't really from an XJ1100.......all of the XS1100 models used similar BS34 carbs, but there are some differences (which can be overcome with parts substitution), and in particular, the "early" BS34's (1978-early 1980 XS1100 models) used a different arrangement for the pilot fuel jet (it draws fuel from the main fuel jet circuit!) and uses a different style pilot fuel jet. None of your photos are up-close enough for me to identify which style BS34 carbs you have, but I thought that I'd point that out.

Also, the specs above are for USA XJ1100's, I'm not sure whether the Canadian models used different (typically, richer....) jetting than the USA models, if there was a difference.

 

Hey Chacal,
Thanks for all that. I'll post some pics later but I'm confident I've got the correct jets, the soda blast exposed everything nicely.

I think you might have found a problem for me. You have the float height as 5mm +-1. The service manual I have says 3mm+-1.

That could certainly explain the problems I'm having. Can I get a look at the source for that? I'm not doubting you and if I've got the wrong info I'd like to have the right data on hand.

Thank-you for posting that!!

 

Whoops.........you are correct, the fuel level is supposed to be 3mm +/- 1mm.........will get that fixed, thanks for noting that error!