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Too much oil in sump


Can anyone help me with this please:

My 57 Dominator 99 seems to have too much oil in the sump.

The return to the tank is a constant heavy flow and the force is enough to blow oil out of the filler if the cap is removed and even though a new cork seal has been fitted to the cap it leaks badly.

The cylinder bores are good and have been lightly honed and new rings fitted.

i seem to lose a fair amount of oil out if the crankcase breather.

all this seems to indicate that there is too much oil getting to the sump

Any ideas 


In reply to by john_hall11


Hi John,

at least if you are stripping you're bike down you will have the opportunity to scrutinise each part to determine if it's standard or not.

I should have guessed that my machine had been got at by the TLS front brake and Borrani rims. I bought it from a dealer who had just changed the oil and cleaned the contact breakers to get it running for sale after it also had stood for some 40 years. I'd hoped to just do a rolling restoration on it to maintain its patina. When I took off the rocker covers to check the valve clearances the first inkling I got was rocker arms which looked as though they'd been chrome plated (very highly polished).

at least if you can determine your machine has standard internals you'll be able to set it up as per the manual.

without a doubt most of my issues have come about because my bike has been tweeked and there are seals etc which I should have replaced because it had been sitting dormant for so long.

Good luck



Thanks Terry, for the money I would change back to a  brand new 376 carb, and try that for a comparison, for £200 it could be a good fix and maybe the blues will go away!

The aperture/choke size is 1 1/8 th I think on the 389 rather than 1 1/16 th on the 376.

Best of luck!

See table attached





Thanks John,

if my machine was standard I'd have no hesitation in fitting a brand new bog standard carb, however it's not and with the changes made to the motor it's bound to need some changes to the carburation.

I guess I'm hoping that someone with a 99 with similar upgrades to mine will read this and tell me what they have fitted carburettor wise.




The 389 size Monobloc carb does not suit the Model 99 except for fast occasions such as track days. From what I have read so far this is what your bike appears to have been set up for. The HC Pistons and Dunstall camshaft all point towards this. The 389 will not allow good idling on an 88 or 99 engine. The air / fuel mix is poor and this can lead to difficult starting and a very lumpy idling and low speed running. Fit a new 376 carb with a 250 or 260 jet instead.

Perhaps I have missed it in the thread but I suspect your engine also has a 6 start oil pump conversion. On a 99 engine this is a waste of time and just leads to over-feeding of the whole engine. The pressure release valve will just dump all the excess oil straight into the timing cover and sump. So the pump scavenge side then has to work overtime to clear. That explains the constant return flow you are getting into the oil tank.

Robert has correctly spotted that the oil rings on your engine have probably not bedded-in enough. You mentioned that the engine bores had been honed. The problem with this is the process can lead to rings not bedding-in properly for ages. This has led to blowby with the knock-on effect of the breather chucking oily vapour all over the place. For owners with an oil tank with a breather connection to it the effect is oil blowing out of the cap. Possibly the blowby has also washed the pistons of oil and led to the partial seizures.

Attachments show an engine crankshaft I have been given to repair. This engine had allegedly been recently fully rebuilt......Really!!!




Is that the same crank as in the June 'Classic Bike' (pg79)? Even if it is, it is a salutary lesson of why oil changes are so important!



The advice about dropping back to a 376 is good as is the 6 start back to 3.

Your engine is tuned for top end power, it loses out at the bottom end which makes it not a good bike for today's roads.

As the engine is modified on cams etc even if you go to the 376 the carb settings will need to be modified to suit the engine.

This is a good guide, note the advice of the carb actually being 5 carbs, mark your hand throttle at 1/4. 1/2, 3/4 and full. Then note the symptoms at each opening and use the guide to alter the appropriate setting.


Five Stages Of An Amal Carburetor:

Stage one: Idle to just off idle Pilot air screw and pilot jet To change: Adjust pilot screw or replace pilot jet

Stage two: 0 to 1/4 Throttle Slide cutaway #2 Rich to #4 Lean To change: Replace slide - change needle jet

Stage three: 1/8 to 1/3 Throttle Needle Jet To change: Replace - change needle jet

Stage four: 1/4 to 3/4 Throttle Needle and Needle jet combination To change: Raise - Lower Needle or replace needle

Stage five: 3/4 to Full Throttle Main Jet To change: Replace main jet

Hi again Robert,

Believe it or not the clutch and the gearbox are excellent on my bike.

Initially I had some issues with the clutch grabbing as I pulled away but this was down to rusty blurred plates and ridges on the splines and latterly a worn centre spider where the shoulder at the end of the splines had all but worn through. Rectifying these issues and fitting new Venhill cables, which I made up myself has given me a lovely smooth light clutch, pity the motor won't follow suit.


Thanks John,

yes I've been working with the Amal set up procedure but am still at the Main jet point really although feel I'm really close. Need to do a proper plug cut after a high throttle opening run just to check out that I'm not too weak at the top end.  I assume that I can do this it high revs in a low gear rather than 100mph in top gear?

I can get the idling set OK but it tends to go off after a run but I put this down to partially fouled plugs. If I clean them it idles OK. (Fitted with B7ES's). However it is looking like I need to go back to a 376 and start again.



Looking for a local bike tuning firm that has a rolling road. Just one or two runs will give you a very good picture of what is going on,  with real data as whether it is rich or lean. And as a bonus you won't get points on your licence! Nowadays they aren't super expensive either.

Regards, George. 


I seem to be making some progress although it's not perfect.

I've now replaced the needle and the needle jet and carried out a test ride of about 10 miles. The bike seemed to run fairly well but still seemed a bit "knocky" when laboured. When the plugs were removed they were very clean which was very encouraging.

Stripped down the motor yet again and fitted the timing disc and reset the ignition to 28 degrees BTDC. Approx 27 on one side and 29 on the other.

Went on a long ride(1hour +) taking in all types of roads at high speeds and country lane low speeds. The knocking is much improved but not gone. It appears that after slow running for a few miles the idling goes off a bit. If I pull over and let it idle it runs very slowly and sometimes dies but if it doesn't then after a minute or so it begins to run fast. 

Initially when I set up the pilot mixture it seems to idle most evenly with the screw almost fully screwed in. I've read that in this condition the pilot jet size needs increasing but I'm a little reluctant to do this as the next size up is a 30 which seems large when you look at those fitted to much larger cc machines. There is also a very, very slight hesitation when opening the throttle from the closed position.

after the run the plugs were slightly sooty but it wiped off easily. I'm not sure if this is because the bike is still running rich or if it's burnt oil.

I've read a few comments on the forum regarding Esso premium causing older machines to run richer, unfortunately this is the fuel I'm using so that's added another dimension to my problem.

The bike stood for about 3 months just before and during the lockdown and I'm wondering if fuel evaporation has gummed up the small pilot drillings (the jet is clear) so the next plan is to strip down the carb completely and check it through. I regularly have this issue with my Ariel VH but know exactly the symptoms and the cure. If I don't find anything I'll have to obtain a larger pilot jet and try that.

any comments appreciated

Terry Guy








Hi Terry, Would be helpful to know what pistons are fitted, Could be 10 to 1 , if so even 28 degrees would not stop it knocking , about 9 to one is the most I would go . The Esso synergy plus will normally be ok if left for months, Keep playing with it.  Years of fun waiting for you!!.


Sooty plugs won't be caused by main jet unless you are on near full throttle. If the pilot needle is set correctly that leaves the slide or needle. I suspect slide since it sounds like your problem remains at quite small throttle openings. A low needle can cause overheating issues through running lean. Dio you have the Amal stage by stage setting instructions? They do work.

And of course there is the old adage that most carb problems are really electrical  and vice versa...though soot sounds like carb!

With the oil issues, is it possible to fit the timed breather wrongly? Not easy to check. But my mag once flooded in winter due, I think, to a mixture of unwisely revving too hard with a wet sump, and (more likely I think) having a breather pipe blocked with emulsified oil plus water in the cold weather.


Thanks Robert & David for your inputs.

as per my last post I removed the carburettor and carefully dismantled it on my bench on a clean sheet of paper in order to spot any dirt or gum etc which could be causing my issues. I took everything apart including pushing out the jet block

it was spotlessly clean and all the tiny pilot drillings were clear. All I could find was what looked like a small bubble (Fish eye) in/on the pilot jet which may have been water I don't know but it cleared when I blew on it. Only other thing I did was to remove a small burr on the slide where the throttle stop sits.

I checked the stay up float for snagging but that seemed fine.

I refitted the carb back to the bike took out the spark plugs (NGK B7ES) and gave them a light wire brush.I also marked up the the throttle to show the slide position.

Then I took the bike out to perform the stage setting sequence. After a few miles to warm it up I took it along a local dual carriageway and carried out the full throttle check for the main jet. Gradually closing the choke made no perceiveable improvement to the acceleration so I think the 250 main jet I fitted is correct. I did this check 3 or 4 times.

then I pulled over to set the pilot mixture. On this occasion adjusting the screw gave a better response than what I had previously and I ended up with a reasonably even idle speed with it screwed out about 2 turns.

Back on the road again I went on to ride another 30 miles on back roads, A roads and dual carriageways and it ran superbly falling back to a nice idle at junctions and smoothly pulling away without any hesitations. As for acceleration it goes like a rocket and that knocking has all but gone. When I got back home I let it idle for a while and then removed the plugs. Guess what they're the correct brown colour with little sooting?

what was the cure:- You tell me. The only thing I can put it down to is that it's taken a while for the new rings and the honed bores to bed in and that plug fouling was causing the poor idling/hesitant pull away condition after a few miles. As for the acceleration knock: I'm not sure if fouled plugs would cause that but I am going to give the auto advance unit another look to make sure it's returning properly.

Fingers crossed that I'll now be able to put on some enjoyable miles at long last.

Thanks everyone for your input and suggestions


A Happy Terry Guy


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