Resurrecting a 72 750

I would clean the float bowls out and check the float levels, ensure you have viton tipped float needles. The pilot jet on these carbs is incorporated in the body of the carb. spray some carb cleaner in the two small holes in the front face of the carb (air filter side) and see where it comes out. Ensure the carbs are balanced with a carb balancer and strobe the ignition timing. even with worn out carbs you should be able to get an even tickover.

Previously nick_ohare wrote:

I just bought a 72 750 off ebay. The previous owner had passed away and his mates were selling his collection on behalf of his widow. The 750 is in very tidy condition and comes with a huge wodge of receipts and old MOTs.

It hasne been on rhe road for 18 months or so and I want to get her running well so I can take her to be MOTd. So far I have drained the fuel out of the FG tank which has been lined, I have removed the drain plugs from the carbs (some crud in one). Oil is coming back to the tank nicely so I decided to fire her up.

Started first kick! great sound tiny puff of smoke and oil returning healthily. However rather rough running wont idle for long however I adjust the throttle stop screws. The idle creeps up and down and will be different when it has been stopped and then restarted. Carbs are Mk1 Amals with K&N filter. My question is, will the old fuel have left nastiness in the carbs? Am I wise to strip and clean them?

Any other things on a check list for getting the old girl ready for the road? Nick

Nick....Is your engine a 'combat' type ? Does it have a small crancase drain plug and the breather chamber between the rear engine plates ? If so it might be worth checking if the sump oil scavenge has been modified, plus the mk.3 breather mod.

Colin

The float needles will have a black rubber tip on them. My guess is that if the previous owner took the time to fit a PW3 cam, he probably had most of the other stuff squared away. Not sure how you would check if the sump oil scavenge has been modified without splitting the cases Colin.

If there are a new pair of carbs fitted and you are lucky they might be Amal Premiers, in which case there should be a screw on the opposite side of the body to the pilot air screw, to gain access to the pilot jet. These carbs are quite well thought of and don't tend to eat themselves as the earlier ones do.

Let us know what you find.

All 72 crankcases have the badly designed sump and breather setup until the MKV was introduced, not having the C stamped on the head does not mean you are ok on the sump front. The check is to look at the underneath of the cases, no big nut for sump drain means you have the problem cases. The problem is the postion of the oil return pickup, it is too far forward so at sustained high revs the oil goes to the back of the crankcase and out through the breather and not the pump, that plus the sump filter being deleted as well.

Fix one is to move the oil return pick up point backwards, at least 3 ways of doing this but all require a full engine stripdown to give access to the oilways. The early fix was to mill a substancial hole away at the rear but latest mod is to instead drill several small holes which then act as a filter of sorts.

The breather can stay where it is but by putting a reed valve just after it you improve the breathing side of things.

Hello again Nick....

Check out this site for details of the crankcase modification at --

The article is quite informative and I used this site when I did the mod on my '72 interstate

Previously david_evans wrote:

The float needles will have a black rubber tip on them. My guess is that if the previous owner took the time to fit a PW3 cam, he probably had most of the other stuff squared away. Not sure how you would check if the sump oil scavenge has been modified without splitting the cases Colin.

One way to check if the mod has been carried out is to go for a long run at sustained 5000 rpm and see if the oil level in the tank has gone down. It might be prudent to carry a catch bottle to drain the sump to enable you to get home !!!

1) You have 850 cases so no worries on the need for messing around there.

2) A 72 will probably have a fibre glass tank, ethanol in todays petrol eats the fibre glass and some of the bits get stuck in the filters, some dissolve in the petrol and then find their way into the carb and block jets and passageways especially the pilot. Some continue further and stick to the inlet valve stem. Best solution is to get a Steel tank, Emgo do a very good Roadster tank.

3) Opps, both should be the same size, what that size should be needs to be determined by a tune up as you have a non standard cam.

4) Good, these are vitron tipped

5) I get my carbs bored out and the slide sleeved, the metals then are different which makes the carb bore and slide wear much slower than on originals, other option is the Amal premiers.

Previously nick_ohare wrote:

Hi John, thanks. It seems that the engine number is indeed a very late 850. I thought that from 73 onwards there was a car type spin on oil filter? There is none with mine.

It is a fibreglass tank which has been lined but there are bubbles appearing under the paint which I suspect are signs of disintegration. Happily I have a spare steel interstate tank I can use while I invest in a steel roadster tank. I cant find Emgo on line except for a US outfit any links for the UK?

Looks like time for new carbs Cheers Nick

The filter fitting is not related to the crankcases, you buy the bits and drill 2 holes in the gearbox cradle for the filter housing mounting bolts, there was a factory kit and my 72 combat with 72 cases has this kit fitted. Not sure who has the Emgo in stock but they are available in the UK, Andover may do them, if not try RGM or Hemmings.

Because of the sludge trap will be working harder when there is no external filter it will fill quicker, as the engine has had at least one rebuild it should be empty or close to empty but an external filter keeps it this way.