Dominator difficult to start

Previously wrote:

Hello , I hope you can help me, I have a 600 dominator 99, It has a SS cylinder head, I believe it is an early one with the inlet and exhaust valves the same diameter, The head has had new valves and guides and seats cut, Also new 930 concentrics, It is very hard to start, Does not seem to be drawing the fuel, If i squirt petrol in the back of the carb it will fire but not without, I have tried the choke in all different positions and tickle them, Could it be a jetting problem, The carbs have 280 main jets and needle in no.2 , When i do get it running it revs out well and ticks over ok, I have a great spark from a competition mag that has been rebuilt, Any advise would be very much apreciated, Kind Regards, Gary

Hello Gary Your lady Engineer to the rescue. Well lets start with the Valve Have they been Ground in correctly .and your carburettor are too big .you need 927 or 928 mk1 concentric .but all 99 models had the mono-bloc carburettors 367/288 and 376/289 with 230 main jet 3.1/2 cut-way side .106.needle position 3 but you need to get a good seal round the valves first. so get lapping in with a lapping stick.with rubber suck on the end valve griding paste fine . you need some engineer blue. to find were the valve are not making a seal .it sound too me like someone as not cut the valve seal faces in right so there maybe some work to there .I wish you could send it to me I would Have it sorted in no time. I did my own valve seal cutting and it did not take long to lap in ether .to do a test remove all springs but not not lose the Collete's take out the valve give the valve seal faces a clean both mating surfaces so there nice and clean. then fit the valve bake in with cylinder head on its rockbox ,once these are in place you then fit two spark pugs .now your ready to do a test have some blue meths or white spirit with a bit of engineers blue mixed in the pour the meths or white spirit in the cylinder head blow and make a level ,so the spirit is around the valve so you then can see if there is any leaks .to a good seal there should be no leaks round the valve from the spirit mixture .if you see it running out of a port this tells you there is a valve not seating right. hope you understand all this and I hope this helps yours Anna J Dixon

A pair of 930s is rather big for a 99, even with an SS head. I wouldn't go for anything bigger than a single 928. Bear in mind that 99s aren't the strongest engines ever and that the con rods are 50 years old. The last thing you want to do is tune it for high power at high revs. Madness that way lies - or at least spectacular blow-ups. Gordon.

Gary what year is your bike? Twin carbs and large inlet valves were optional on '59 Model 99s so if it is of that era that may be what you have, some people 'assume' an SS head because of the twin carbs. As Anna says they would have been Monobloc 376/67 but would not have been handed I don't think - I am ready to be corrected on that one.

If it fires when you squirt petrol into the back of the carbs and then runs ok it doesn't sound too far out. When you tickle them are you sure the bowls are filling up? Are you doing it until your finger is getting wet? I don't know anything about concentrics but as far as I know the procedure would be the same. I would check that first if I were you.

Previously wrote:

Gary what year is your bike? Twin carbs and large inlet valves were optional on '59 Model 99s so if it is of that era that may be what you have, some people 'assume' an SS head because of the twin carbs. As Anna says they would have been Monobloc 376/67 but would not have been handed I don't think - I am ready to be corrected on that one.

If it fires when you squirt petrol into the back of the carbs and then runs ok it doesn't sound too far out. When you tickle them are you sure the bowls are filling up? Are you doing it until your finger is getting wet? I don't know anything about concentrics but as far as I know the procedure would be the same. I would check that first if I were you.

I do not think its anything to do with the Carburettor .you can put nitro down the carb and it would not start its the valve are not seating . because there very little in the way of compression !

If your bike runs and ticks over, there should be nothing much wrong with the top end. Some concentrics are known to have pilot drilling problems. I would check the carbs carefully to make sure that all is well there. I would also make quite sure that all is well with the ignition side. Try different spark plugs, keep the gap down to about .018". A 99 should start easily. Is the head a downdraught or is it a standard head with a twin carb adaptor? Gordon.

Hello,have you tried to tickle and full choke andNOT touching the throttle?I have seen a lot of trouble starting when people opens the throttle to much on cold engines! Just a simple tip. Good luck!!!

Best regards from Svein at acold Norway.

It sounds like your float levels are too low. Worth a check. And you do have chokes fitted, don't you? I would suggest that for a standard Domi head, a pair of 930s are really too big. Once it is started and warm, I presume you are adjusting the slow running as per the book. If there is a problem with the pilot jet drillings, you will be able to get a tickover BUT fiddling with the pilot air screws won't make any difference and cold starting will be difficult. Is your comp mag fixed advance? That wouldn't help. Gordon.

Good advice from Gordon. It is always worth checking float levels. I have just rebuilt an ancient Yamaha two stroke (excuse the heresy). I eventually got to the point where I thought I had corrected all the problems caused by the previous owner but it would not start easily or run satisfactorily. Logic pointed to a fuelling problem but I had only an old Haynes manual that provided minimal carburettor data. Luckily a genuine service manual for the correct year surfaced on Ebay. I checked the float level and it was 2.5mm low. Fixed it and the bike now starts and runs well.

I've just re-read all this and I have a couple of questions. What are the spark plugs and have you checked the pilot jets by squirting some carb cleaner or similar through them? You should see a fine mist come through if they are clear. Have you checked for a manifold air leak? One unlikely possibility, but I have seen it, is an air leak on the manifold that closes up when the bike warms up.

I wouldn't go spending money on new carbs just yet and I wouldn't worry about the main jet. It has little bearing on your starting problem and in any case as the bike runs OK once started, it is easy enough to do a plug chop to check it.

Gary,

You are getting a lot of useful comments but none seem to be the answer.

My thoughts for what it is worth; until you squirt fuel into the carbs (both or just one?) the engine will not fire; so it must be lack of fuel.

Once running and warm/hot it will start.

Cold engines need a rich mixture to get them away that's why carburettors have chokes, so again it seems to be lack of fuel.

When it is running is the mixture weak or rich, what colour are the plugs?

I dont know that much about concentrics, why not call Amal and ask for their advice.

Good luck

Tony

My 99 starts first or second kick even if left for years,always needs full choke plus a tickle. squirt a bit of fuel down each carb, if it works then you can forget the motor.Twin carbs are a waste of time on an old 99 as you do not want to be thrashing it unless you have modern con rods.

I agree with Alan - don't buy new carbs yet. It does seem like a fuelling problem. I have run my 99 on a single 928 with no problems whatsoever. The carb size won't affect starting. However, I would make doubly sure that the ignition side is OK. Pop in a couple of NGK B7ES plugs in just to be quite sure (gap the plugs at 0.018). I have had problems with Champions both in the past and recently. Disconnect and blank the balance pipe and try fuel down one carb at a time. If it's a carb problem, you wouldn't expect both to be amiss. But it could happen. It should start happily with choke shut, a tickle, a hint of throttle and one or two kicks. Can you borrow a carb and see what happens with a known good one? Even just changing one should get it started on one at least.

Previously wrote:

Thanks for your replies, I have had a chat with Amal and they think my problem is I am not getting enough suck because of the 930's and the balance pipe, My friend is having the 930's so i have ordered some 928's and will blank off the balance pipe, Will let you know how i get on , Gary

Hello Gary I thrown more NGK plug in the bin than any other spark plug I've been riding bike for the best part of 40 years And the best spark plug I have come across is Bosch W7DTC .this is whats in my 650cc Manxman Now and as been of the last 3 years starting is no trouble.and the engine runs very clean , I have Not changed My oil for over a year and its still as clean as it was put in. its all ways checked before going out too ride is. and it still a magneto as it was built 53 years ago . so this counts for something right so good spark plug mean clean running engine with more power and more mile to the gallon and good top speed if needed . you need to keep you bike clean inside as well as out side. yours anna j

Hi Gary - with cars and bikes I've found that those symptons were usuallyignition or valve timing.You say you get a good spark? The best way to test that is by takinga plug out, connecting the HT lead to it and get someone to kick the bike over whilst you earth the plug against the head and see it there's a strong spark actually at the plug end. Best done in the shade or in the dark. Evena good spark won't start the engine if the timing is way out. Obviously changing the plugs is another process of elimination, as has been suggested. The leads and caps should be non-resistor type for a magneto with new, plain copper-cored leads.

There wasn't any "SS" head with the inlet & exhaust valves the same size as far as I remember. Mine is a July 1959 '99' which had the optionaltwin carbs ex-workswith the optional, large inlet valve head. (These were standard from 1960 onwards but were fitted with single or twin carbs according to the model). It sounds like someone had just put twin carbs on a standard, pre-1960 head. If you try starting without squirting any additional fuel, check the plugs after, say, 4 or 5 kicks without starting. If they are wet then fuel is reaching them - if only damp then it isn't.

If a bike (or car)starts easily from cold without choke then it's running too rich. I'm with Gordon and others in thinking it isn't worth going with twin carbs on a bike that age. I've de-tuned mine from it's original (upgraded by me at the time) 9:1 pistons down to 8:1 or thereabouts (haven't checked it yet!)

Good luck! Lionel

Hi Gary, I've sent you a private message to see if you liveclose enough tome that Imight help.