Project "walrus" Yam XS 750

2_DONE_THE_TON

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Hey guys!

It´s been a long time coming.
I have a (two) new projects.After “finishing” my RD250 to RD350 conversion and different mods I got hungry again to find me a totally different project bike.
Since I´m always looking for something “exotic” I found two Yamaha XS 750´s.
The PO completely modified a small apartement in an old house (and with old I mean around 1890) to a small and extremely dense workshop with 100 per cent Yamaha Triple dominance.
All walls were filled with tools, pin ups from the 90´s and parts and stuff for the Yamaha Triples.
He offered me two completely stock 750´s for a good price together with many parts for example a 3-1 exhaust setup and a 826 cylinder and jug kit (with the right head gasket).
Problem was he couldn´t start the XS´s, one is just a part bike so it needs motor work but the other one should get started this weekend.
So its been really short but I already have questions:
.) Is there a way to check for the 2nd gear issue on this bike without running the bike on the street (he told me that I can shift trough the gears by hand if I want)?
.)is the second gear fix an easy fix or should I walk away in this case from this deal?
.)he used 850 parts to change from the stock points ignition to electronic ignition.is there a way to check if its properly working without running the bike on the street?

I hope you guys can help!
I will post pics soon!
 

2_DONE_THE_TON

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Re: Project "walrus" Yam XS 750

So it happened.I couldnt resist and bought two xs 750's.
One is in a nearly original condition and quite crusty :)
First plan is the get the original one to start and at the same time slowly modify the crusty one.
I'm currently in the process of cleaning the carbs,any help appreciated!
 

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datadavid

New Member
Re: Project "walrus" Yam XS 750

I can clean your carbs And make them work flawlessly, all i need is a dirty look from the lady in red
 

2_DONE_THE_TON

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Re: Project "walrus" Yam XS 750

datadavid said:
I can clean your carbs And make them work flawlessly, all i need is a dirty look from the lady in red
;D ;D ;D hahaha youre epic man!


back to the carbs..:):

there basically broken down to the carb bodies (i dont want to break the 3 carbs apart, hope i can keep em together.
I sprayed trough every air bore and jet with carb cleaner and pressurized air, membranes look mint, slides with the needles attached have slight scratches.
one of the cylinder 3 floats was even broken and just sitting in the there.
do i need to remove the choke mechanism too to clean the bores?
thought about putting the whole bench to ultrasonic...
 

datadavid

New Member
You dont need to take them apart unless for changing the butterfly seals. Just go through all the jets and passages and hold up all the diaphragms against a strong light, if it shines through they are shot. Can be mended with a gas proof vulcanizing rubber glue, since they are high $ parts. Only way for you to test if butterfly seals are tight is to put them back on the bike after cleaning and shooting some motor starter at them. You will notice the engine rpm increase if they leak.
 

datadavid

New Member
Re: Project "walrus" Yam XS 750

Now go bolt them up and crank it! That is if you have changed all the fluids first..
 

2_DONE_THE_TON

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datadavid said:
You dont need to take them apart unless for changing the butterfly seals. Just go through all the jets and passages and hold up all the diaphragms against a strong light, if it shines through they are shot. Can be mended with a gas proof vulcanizing rubber glue, since they are high $ parts. Only way for you to test if butterfly seals are tight is to put them back on the bike after cleaning and shooting some motor starter at them. You will notice the engine rpm increase if they leak.
I´m pretty lucky...the membranes seem spotless (checked them vigorously since this was the problem on my KZ400 back then, quite agonizing...)

Mains are: 145´s and idles are 17.5´s...
Am i right that you mean shooting the brake fluid "between" the carbs where the butterlfy axles meet the carb bodies?
I will let the engine run warm and then make an oil change (motor oil and shaft oil).
probably need to change the rubber mounting boots of the carbs too, they look hard and worn,do you know what the stock mixture screw setting is (I write down the turns out of the screws they were 5 1/4 turns out)?

do i need to bench sync the buterflies with some copper wire?
in closed position there seems to be NO gap between carb body and butterflies now...

thanks for your advice so far!
 

datadavid

New Member
Idle is governed by the mixture screws. They should be 1- 2 full 360 degree turns out. Pilot jets Should be bigger than 17.5! More like 42.5...
It does not sound right.. will dig out my old carb corpses when im back in the garage. Doing this now:
coffee and admiration! :D
 

2_DONE_THE_TON

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thanks for your effort man :)!

just looked up for the carb boots, there seem to be different lengths?!does it matter which one to use or should i stay strict to the stock ones?
 

datadavid

New Member
Re: Project "walrus" Yam XS 750

Ryan Stecken said:
thanks for your effort man :)!

just looked up for the carb boots, there seem to be different lengths?!does it matter which one to use or should i stay strict to the stock ones?
Depends on your other carb mounts i guess? maybe hang them in there w/o boots and take a measure?
 

datadavid

New Member
show me yours i'll show you mine
so these are my main and pilot jets, this would be the stock jetting of a 78 something model.
42.5 pilot 130 main.
You are going to end up at 140 mains, 142.5 center main is nice also - if you are running open exhaust and good flowing filters. May want to raise the needle one full notch as well, but do that last. I did not need to go up on pilot jets on my stock-ish (pod filters and 2" 3-1 megaphone) 750, it ran perfectly on stock pilot jets.
I run 150 mains and 155 center in mine because its got high comp ratio, full open exhaust and k&n filters besides the extra 150cc
 

Psycrow

Member
Re: Project "walrus" Yam XS 750

Also working on an XS750 triple 78' over in the Tracker section... I'll be watching this.. I've delta with Second gear issues on other Yamaha bikes... my understanding is that it's not a terrible job on these... on my 84 FJ1100 it was a complete teardown and split cases to change two gears and a shift fork... geesh. Unfortunately you will need to drive the bike and load second gear to see if yours has the issue... it's not an expensive fix if you do the work yourself and the bike can still be driven till you decide to do the repair. Your not going to ruin anything else by riding it... just take it easy through 2nd.

Psy

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XS750AU

Member
Mains are: 145´s and idles are 17.5´s...
Am i right that you mean shooting the brake fluid "between" the carbs where the butterlfy axles meet the carb bodies?
I will let the engine run warm and then make an oil change (motor oil and shaft oil).
probably need to change the rubber mounting boots of the carbs too, they look hard and worn,do you know what the stock mixture screw setting is (I write down the turns out of the screws they were 5 1/4 turns out)?

do i need to bench sync the buterflies with some copper wire?
in closed position there seems to be NO gap between carb body and butterflies now...

Hi Ryan
145 mains and 17.5 pilots were standard in some markets, but as Dave has said 130 & 42.5 is a common arrangement.
Not sure about shooting brake fluid - but to check for leaking seals and mounting rubbers I have used carbi cleaner. You can smell it come through the exhaust. The fact that the mixture screws were turned out 5+ turns indicates that the PO had idle problems due to air leaks and they were trying to make the idle mixture richer. Suggest you get a new set of rubber mounting boots from Yambits in England (cheapest I could find) and butterfly seals from Mike XS. Made a world of difference to my XS750.

At idle there should not be any visible gap between butterfly and body, when the idle speed screw is fully backed off. This may be another pointer that your bike was sucking air through a leak and the PO was trying to get it to idle below 2,000rpm. I had the problem and it has now been fixed by butterfly seals and new rubber mounting boots - it is 40 years old!!!
Good luck
Tim
 

XS750AU

Member
Hi Ryan
Just looking at the photos and looks like a 2D and they had triple points ignition!!! A bitch to maintain.
Has it been converted to the later CDI???
Don't mean to tell you how to such eggs - but have you tested that you have spark?
Cheers
Tim
 

2_DONE_THE_TON

Active Member
DTT BOTM WINNER
datadavid said:
show me yours i'll show you mine
so these are my main and pilot jets, this would be the stock jetting of a 78 something model.
42.5 pilot 130 main.
You are going to end up at 140 mains, 142.5 center main is nice also - if you are running open exhaust and good flowing filters. May want to raise the needle one full notch as well, but do that last. I did not need to go up on pilot jets on my stock-ish (pod filters and 2" 3-1 megaphone) 750, it ran perfectly on stock pilot jets.
I run 150 mains and 155 center in mine because its got high comp ratio, full open exhaust and k&n filters besides the extra 150cc
thanks datadavid for your input!

looks like you have different carbs...my mains and idles are installed in the float bowls...looked it up and my settings are stock for my model...
 

2_DONE_THE_TON

Active Member
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XS750AU said:
Hi Ryan
Just looking at the photos and looks like a 2D and they had triple points ignition!!! A bitch to maintain.
Has it been converted to the later CDI???
Don't mean to tell you how to such eggs - but have you tested that you have spark?
Cheers
Tim
thanks for your insight tim!
the PO converted it to the 850 cdi setup...i have strong spark.this was one of my concerns...is it possible that the timing is off, even when the PO installed a cdi?if yes how can I check?
 

2_DONE_THE_TON

Active Member
DTT BOTM WINNER
Re: Project "walrus" Yam XS 750

I have another question guys concerning the stock brakes:

They are stuck so i'll nees to get them off and give them a good clean...there are three bolts holding the brakes,one has some kind of a rubber dampening to the screw...what is that screw doing?is it also holding the brake on the fork?
Just wanted to ask tou guys before i break something precious ;-)
 

XS750AU

Member
Re: Project "walrus" Yam XS 750

Hi Ryan
Difficult to install cdi the wrong way. The main thing to check is that the rotor is correctly engaged in the idex pin on the end of the crank. Also check that the index pin has not been push flush with the crank. Should run at that point, then you need a timing light to get the coil plate exactly correct.
Brakes, 2 bolts hold the brake assembly to the forks, undo first. The bolt with rubber damper allows the caliper to float and self align with the disc. You can rebuild without removing. but if you are re building pull apart and make sure the caliper can slide on bolt.
Cheers
Tim

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XS750AU

Member
Re: Project "walrus" Yam XS 750

Hi Ryan
You say your jets screw into the float bowl! That sounds like the Hitachi carbies used on the 850. The 850 cdi is great as it has electronic advance, but the Hitachi carbs have a bad rap. Hard to get parts including jets. What brand is marked on them?
What carbs are on the other bike, they may be a better option. Makuni series II with the 2 position choke are the best factory carb unless you go the triumph option. If you go the triumph option you will need to rejet as yours is a 750 and the triumph triples with carbs were 900.
Regards
Tim

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datadavid

New Member
Re: Project "walrus" Yam XS 750

Yes throw the hitachis as far as you can. Not worth the bother.
 

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