I guess this works pretty much for all motorcycle carburetors. Take them off and give them a good clean.
The problem with the XS750 is that the previous rider mentioned that when the engine ran it felt a bit lumpy which he suspected the carburetors were causing the issue. Its an old bike and since we were having issues starting the bike it seemed logical that we’d need to check the carbs anyway whilst we waited for parts to arrive.
Removing the carbs
First things first – test to see if the petcocks are working, the bike draws in fuel through the carburetors by using a vacuum. So if we remove the fuel feed hoses that run to the back of the carbs, there are two of them split between the three carbs, we should be able to turn the petcocks to on/fuel and nothing should drip out – turn the petcocks to prime or reserve and it should start draining the fuel from the tank. To get to the hoses you may need to remove the air filters first -held on with jubilee clips.
The bonus is we now know that the fuel lines and taps are working as they should. The carburetors on the XS750 are sealed on using jubilee clips, loosen these and you should be able to wiggle the carbs free of the engine block – it will take a bit of effort and a long screwdriver to get to the central carb.
So we’ve removed the carbs, have a bucket on standby to empty the majority of the fuel out into – may take a while to get the most out. We can also remove any remaining air filters – you may want to change them, ours look fairly new so no need. Now we can work on the carbs separately and in the warmth of indoors – just use a container to in case of further spillages.
Stripping the carbs down
We looking for issues such as build of petrol deposits – petrol can cause a varnish to appear on the inside of the carbs and can also create what can only be described as gunk. We’re also looking for any signs of wear on the needles, seals and float chambers along with any of the diaphragms perishing.
First thing we noticed the bolts on the top of the carbs were very worn and rusted – so we’ll end up getting a new set of bolts. With our favourite tool, the mallet, we hammered in a screwdriver to get a better purchase on the bolt head and between two of us we forced each bolt out. Otherwise we would have probably had to drill the bolts out.
Inspecting inside the tops showed no immediate problems, everything looked fine here and looking through the carbs showed that they were very clean. So we proceeded to remove the base of each carb and inspect the float chamber.
In here we could see the gasket seals had perished and after removing the float chambers – using a nail and a hammer to aid removing the hinge pin, we could see each float value and filter was very blocked, inspecting further into each fuel line we found dark heavy slimey deposits. With the carbs otherwise looking clean and in good condition considering the age, I think we found our problem.
Solution – get some carb cleaner (Redux etc…) and soak through the fuel lines that run in to the float chambers via the float needle. We’ve left this for a few days to soak through and also soaking the gause filters for each float chamber will also be a good idea.
Refurbishing the carbs
We’ve got a refurb kit for each carb which is a new needle, float chamber gasket and 10mm threaded bolt/seat for each float needle – nothing else seems to be needed so when the carbs are done soaking, we’ve cleaned them and once we’ve got the replacement bolts we’ll fit the new parts.
I was going to follow up with a separate post but it was pretty simple to refurb the carbs. Just follow whats already there and make sure that they’re cleaned.
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