Author Topic: MK5 Starting  (Read 3108 times)

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Offline digcot65

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MK5 Starting
« on: 30 Mar 2018 at 12:09 »
Happy Easter to all, I tried to start the MK5 this morning for the first time, after all the work seemed to be finished.The bike starts, but only on quite wide open throttle and then it is only running on the LH cyl.Both cyl are about 120lbs compression, there are new plug leads and caps and the plugs have been cleaned and the spark looks good, all tappets are set right.I have had both carbs.ultrasonically cleaned and there are new main jets in both.I noticed when I kick it over, there is blowback from the RH carb.Finally, I have tried everything to stop the LH carb from leaking petrol from the small vent in the cap The needle seats before the tickler button can interfere  Any suggestions.Len
Just found a bit more re the running.If I manage to start it and open the throttle wide then the bike revs up and it fires on both cylinders.You can see the exhaust gases coming out of both pipes.
Has anyone else had the problem of the one carb leaking fuel from the top vent, pointing to the needle not sealing Surrey Cycles said they can supply a new float chamber from another Amal carb, but it is 50mm dia. as compared to 40mm dia. of the 274s.
« Last Edit: 30 Mar 2018 at 14:33 by digcot65 »

Offline Rex

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Re: MK5 Starting
« Reply #1 on: 30 Mar 2018 at 16:17 »
Still points to having a blocked drilling on the affected cylinder side. 

Offline Hampshirebiker

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Re: MK5 Starting
« Reply #2 on: 30 Mar 2018 at 16:44 »
It's a pity we can't follow the carb. saga through one topic. However I agree with Rex, it's most likely one of the drillings in the jet block crudded up. Soak in thinners (the jet block) for a couple of days & blow through with an air line & nozzle. I've been there & got the diploma.
Get a new float & needle, I can't see why you need a new chamber. A flooding carb. is really a common sense problem.

Offline digcot65

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Re: MK5 Starting
« Reply #3 on: 30 Mar 2018 at 16:56 »
You tell me how to stop it flooding then .Iv`e had the carbs ultrasonically cleaned and then I blew them through they looked OK but I will check again.The other point is you cannot get the floats or needles any longer,that is the  first thing I tried to get. Len

Offline eddie

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Re: MK5 Starting
« Reply #4 on: 30 Mar 2018 at 17:30 »
Let's try a little common sense! Swap the floats over - if the flooding problem follows the float, then the float has a fault. If the fault stays on the same carb, then the fault is in the float chamber.

  Eddie.

Offline digcot65

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Re: MK5 Starting
« Reply #5 on: 30 Mar 2018 at 17:37 »
Tried that a few days ago, still LH flooding

Offline digcot65

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Re: MK5 Starting
« Reply #6 on: 30 Mar 2018 at 17:40 »
I tried about 6 companies who deal in Amal carbs and they all said that the floats and needles for the 274 are no longer available.I know I could fit the chamber form a 276 carb, it is 50mm dia as compared to 40m dia .but I have been told they will fitso long as there is clearance between the carb and the engine, which there is

Offline eddie

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Re: MK5 Starting
« Reply #7 on: 30 Mar 2018 at 17:44 »
OK, now try swapping just the float chamber top.

  Eddie.

Offline digcot65

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Re: MK5 Starting
« Reply #8 on: 30 Mar 2018 at 17:48 »
Will do tomorrow, my wife says I have spent long enough in the garage.But if swapping the top, does change the fault to the other side, what then as spares are not available

Offline Hampshirebiker

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Re: MK5 Starting
« Reply #9 on: 30 Mar 2018 at 18:05 »
I've just skinned over your float topic. Needle soldered into the float. Perhaps the weight of the solder is affecting it's buoyancy. If the R/H one isn't soldered, swap them over.
Also, take the float top off & hold the float & needle into the inlet bush (vertically). Turn on the petrol & see if it's sealing properly. I'm sure you can find a S/H float somewhere.
I know these old 274s are a sod & prone to incontinence, but as I said earlier the float arrangement is so simple.

Offline digcot65

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Re: MK5 Starting
« Reply #10 on: 31 Mar 2018 at 08:18 »
It s a pity, that it isn`t possible to buy the spares for the 274.I`ve tried so many companies it is obvious there aren`t any left It is also a bit of a gamble to buy an old carb off Ebay or similar. Len

Offline phil1

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Re: MK5 Starting
« Reply #11 on: 31 Mar 2018 at 08:43 »
I had a similar problem. the bike ran on one cylinder and refused to run on two until I opened the throttle up about half way. however this resulted in a lot of back firing. I resolved the problem by replacing the carb body as well as the throttle slide and managed to source a replacement needle from Martin Bratby (tel; 01543572583)   

Offline digcot65

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Re: MK5 Starting
« Reply #12 on: 31 Mar 2018 at 11:55 »
Thanks, I will give Martin a call when the holiday is over. I am soaking the throttle body in cellulose thinners at the moment.I had the carbs ultrasonically cleaned, but members think it still may have blockages in it. Len

Offline digcot65

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Re: MK5 Starting
« Reply #13 on: 31 Mar 2018 at 11:55 »
Thanks, I will give Martin a call when the holiday is over. I am soaking the throttle body in cellulose thinners at the moment.I had the carbs ultrasonically cleaned, but members think it still may have blockages in it. Len

Offline phil1

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Re: MK5 Starting
« Reply #14 on: 02 Apr 2018 at 13:35 »
Hi 65, my mk v is running really well with a steady tick over since I changed the throttle slide and carb body you may getaway with just a new slide it makes a lot of difference to the slow running. I have been plagued with a dragging clutch just would not free properly, so have had to make a replacement pressure plate as the old one was no longer flat by at least  two mm, am weighting for it to stop raining. phil1.   

Offline digcot65

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Re: MK5 Starting
« Reply #15 on: 02 Apr 2018 at 14:57 »
Where did you find a carb .body and throttle slide Len

Offline digcot65

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Re: MK5 Starting
« Reply #16 on: 03 Apr 2018 at 08:45 »
I have replaced the carbs and just changed the floats over and so far neither is flooding.Now it seems to start easier but does not run on the RH side unless I open the throttle wide, then it fires on both.You can see and feel the difference on the exhaust outlet.
I am going to swap the carbs over to see if the fault swaps sides, will let you know in a   couple of frustrating hours time. Len

Offline eddie

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Re: MK5 Starting
« Reply #17 on: 03 Apr 2018 at 08:57 »
Len,
       Wind up the throttle stop screw on the LH carb so that the engine will just keep ticking over on the LH cylinder. Then play with the throttle stop and air screw on the RH carb until the RH cylinder picks up. Then adjust the 2 throttle stops to get even running on both cylinders. When you have achieved this, you can adjust the throttle cables so that both cylinders pick up together.

  Eddie.

Offline digcot65

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Re: MK5 Starting
« Reply #18 on: 03 Apr 2018 at 09:37 »
Thanks for the advice.I have just swapped the carbs over to see if the fault changes sides, I haven`t tried it yet but since I have changed them now I will see what happens.I will then do as you suggest Len

Offline digcot65

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Re: MK5 Starting
« Reply #19 on: 03 Apr 2018 at 10:33 »
As I said earlier I swapped the floats over and it appears to have stopped the flooding, even after you have tickled the carbs it came out of the vent and then stops.I tried changing the carbs over but I was unable to start the bike, so I changed back to the original set up This was to set it up as Eddie suggested, I kicked it over and straight away it runs on both cylinders, slightly more pressure now out of the LH exhaust rather than the RH,but it ticks over and revs nicely.I think it is lulling me into a sense of false security.

Offline tck

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Re: MK5 Starting
« Reply #20 on: 03 Apr 2018 at 11:37 »
Look you just got it get out and ride it
 you are bound to find loads more to do dont spend all that riding time in the garage
put MIKUNI in the search box  read all about fitting them get a couple of modern Mikuni carbs off ebay for peanuts
enjoy your new machine then have a big session in the off season not only will you have located your carb bits but you will have time for all those other jobs you havent found yet

Offline digcot65

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Re: MK5 Starting
« Reply #21 on: 03 Apr 2018 at 18:35 »
Should I look for any particular model or type of Mikuni carbs