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350TSS · 28-02-2018, 02:27 PM

6 inches of snow on ground today and my cold that just will not die meant no time in the actual garage. I managed however, to make myself unpopular with SWMBO by stripping and re-building carburettors on the kitchen table where it was at least reasonably warm.
About a year ago I found some new Mikunis on a forum for £80, originally, I intended them for my 750SS which has the same problem as the M900, namely a seized and sheared slow running jet in one of the pair. The little rubber protective bung goes AWOL and the crud gets in and when you try to adjust them they are seized solid and the brass flats on the jet shear off.
The carbs I acquired I think are for a 750 as they have both electric heaters and the four tapped holes in the float bowl for the oil pipe heaters. One of the electric heaters is missing a terminal post which is probably why I got them cheap.
My M900 has a dynajet kit which I wanted to retain so I stripped down the old carbs measuring float heights and recording jet sizes as I went.
I then moved onto the “new” (750?) carbs, and immediately hit a problem with the float bowl screws on one carb which had obviously never been off before, the heads on 3 of the screws were made of cheese and the cross heads were very quickly and amorphous shapeless dent. I now have 2 sets of carburettors that are useless.
I gingerly tried an impact driver but was very conscious that the force was being transmitted to carburettor metal and I did not want to distort the diaphragm seating flange on the other side of the carb. One came out with the impact driver, one with a small pair of mole grips and one after I cut a slot in the head with a hacksaw and it finally gave way.
My measurement of float heights was consistent across both sets of carbs but I am not sure if I am doing it right. My technique was to invert the carburettor and measure from the face of the float bowl to the lowest point at the bottom of the float – at this point the float is resting on the needle valve but not shutting it. I then pushed the float down until the needle valve was just shut and measured again.
The M900 measured as follows:
LH resting 13.8mm RH resting 13.2mm
LH shut 9.8mm RH shut 7.8mm
The “new” carbs came out as follows – these would appear to be factory settings as they have not been open before
LH resting 11.6mm RH resting 11.7mm
LH shut 7.7mm RH shut 7.8mm.
I only managed to find 3 jets with that had screwdriver slots to remove them, a short one about 10mm round which had the number 70 on it (both sets of carbs) the threaded portion held down a clip which had another jet with an O ring on it (with 150 on it for the M900 and 132.5 for the 750 carbs) and a thin conical jet with 40 on it for both sets of carbs. The 750 set also had jets which fed the underside of the diaphragm but I could not get the equivalent M900 ones out.
The question now is what do I do about carb icing, as I see it I have 4 options
1. install the oil heater pipes and the electric heaters, if I can get a new one to replace the broken one
2. Install only the oil pipes
3. Install only the electric heaters
4. Leave both out altogether
Any option involving the oil pipes will be messy aesthetically, but if I do not fit them I will have to find some way of bunging up the holes in the float bowls.
The electric option is dependent upon getting hold of a heater (no idea how difficult that is going to be) and it would be good to know before I button up the loom in the next day or so.
Leaving out both is an option because judging by comments on here neither is positively viewed as a solution and my usage will definitely be on warmer days.
What would you do?

28-02-2018, 02:27 PM	#573
350TSS Too much time on my hands member Join Date: Jan 2013 Location: Shipbourne Bike: M900 Posts: 1,420	6 inches of snow on ground today and my cold that just will not die meant no time in the actual garage. I managed however, to make myself unpopular with SWMBO by stripping and re-building carburettors on the kitchen table where it was at least reasonably warm. About a year ago I found some new Mikunis on a forum for £80, originally, I intended them for my 750SS which has the same problem as the M900, namely a seized and sheared slow running jet in one of the pair. The little rubber protective bung goes AWOL and the crud gets in and when you try to adjust them they are seized solid and the brass flats on the jet shear off. The carbs I acquired I think are for a 750 as they have both electric heaters and the four tapped holes in the float bowl for the oil pipe heaters. One of the electric heaters is missing a terminal post which is probably why I got them cheap. My M900 has a dynajet kit which I wanted to retain so I stripped down the old carbs measuring float heights and recording jet sizes as I went. I then moved onto the “new” (750?) carbs, and immediately hit a problem with the float bowl screws on one carb which had obviously never been off before, the heads on 3 of the screws were made of cheese and the cross heads were very quickly and amorphous shapeless dent. I now have 2 sets of carburettors that are useless. I gingerly tried an impact driver but was very conscious that the force was being transmitted to carburettor metal and I did not want to distort the diaphragm seating flange on the other side of the carb. One came out with the impact driver, one with a small pair of mole grips and one after I cut a slot in the head with a hacksaw and it finally gave way. My measurement of float heights was consistent across both sets of carbs but I am not sure if I am doing it right. My technique was to invert the carburettor and measure from the face of the float bowl to the lowest point at the bottom of the float – at this point the float is resting on the needle valve but not shutting it. I then pushed the float down until the needle valve was just shut and measured again. The M900 measured as follows: LH resting 13.8mm RH resting 13.2mm LH shut 9.8mm RH shut 7.8mm The “new” carbs came out as follows – these would appear to be factory settings as they have not been open before LH resting 11.6mm RH resting 11.7mm LH shut 7.7mm RH shut 7.8mm. I only managed to find 3 jets with that had screwdriver slots to remove them, a short one about 10mm round which had the number 70 on it (both sets of carbs) the threaded portion held down a clip which had another jet with an O ring on it (with 150 on it for the M900 and 132.5 for the 750 carbs) and a thin conical jet with 40 on it for both sets of carbs. The 750 set also had jets which fed the underside of the diaphragm but I could not get the equivalent M900 ones out. The question now is what do I do about carb icing, as I see it I have 4 options 1. install the oil heater pipes and the electric heaters, if I can get a new one to replace the broken one 2. Install only the oil pipes 3. Install only the electric heaters 4. Leave both out altogether Any option involving the oil pipes will be messy aesthetically, but if I do not fit them I will have to find some way of bunging up the holes in the float bowls. The electric option is dependent upon getting hold of a heater (no idea how difficult that is going to be) and it would be good to know before I button up the loom in the next day or so. Leaving out both is an option because judging by comments on here neither is positively viewed as a solution and my usage will definitely be on warmer days. What would you do?