Ducati.ms - The Ultimate Ducati Forum banner

1 - 20 of 62 Posts

·
Registered
Joined
·
36 Posts
Discussion Starter #1
My 93 750ss is a stellar performer if I ride like I'm in a race, absolutely perfect but, cruising at low revs it breaks up until I rev it and clear it. I also get an occasional pop back through the carbs. Had the carbs cleaned but not sure it was done right. Any suggestions will be appreciated. I want to be able to cruise easy when I want, although I am getting hooked on riding fast. Arch
 

·
Registered
Joined
·
36 Posts
Discussion Starter #3
Thank you, at all rpm it breaks up if not accelerating, After vigorus acceleration it clears up for a short time. It also clears for a short time if I rev it. Don’t know what jets I have. Stock airbox with a K&N fully exposed, the top of the air box is open. Conti silencers. Not sure about the carb clean because the mechanic was sloppy and broke a fairing, fender mounts cracked, left a ground wire off and lost a fairing bolt. So I don’t have confidence in him. I reconnected the ground from the regulator to the neg battery, got some improvement, then added 1 can of seafoam to 1 gal of gas and it stopped most of the breakup at low revs between 1 and 4000 but got worse at high revs. Im thinking maybe pilot jets are dirty. Much thanks, Art
 

·
Premium Member
Joined
·
4,142 Posts
Put a solid (stock) airbox lid on first and see if it gets better. You need a jet kit if you plan on running a open airbox so you need to find out what you have first. You want to diagnose it BEFORE taking it apart.

test with a closed airbox and see if it is better or worse.

Remove filter and accelerate bike to see if the throttle slides are both opening the same .

If you are riding where it is bad and you give it a little more fuel with your enricheners does it get better or worse as you add fuel.

After all those tests you will take it apart looking for jetting to be cleaned, changed or fixes from bad mechanics.
 

·
Registered
Joined
·
36 Posts
Discussion Starter #5
Thanks ducvet, I will look for a proper airbox cover. It does get better when I add fuel with the throttle, not sure what the enrichers are. Best regards
 

·
Premium Member
Joined
·
4,142 Posts
If richening things up helps the bike is telling you that it is lean, this could be due to several things.

1. the pilot jets or fuel screw ports are clogged.

2. the jetting is too lean for the setup you have.

3. something is simply not set right

Start by verifying with a closed lid and if it fixes things you are done, if it does not fix things but improves them you will go in the carbs to figure out why yo are lean.
 

·
Registered
Joined
·
36 Posts
Discussion Starter #10
Hello ducvet, It's been a while because I had some veins stripped from leg and couldn't test my bike until now, but I put on the correct airbox cover and the bike is definitely running better and cooler but it still starts to misfire intermittently when cruising at low rpm around 3k until I rev it and clear it out then its ok for a short while. At higher revs above 4k it now runs great. Is this normal or could it be carbs or valves. I'm thinking the lean condition may have affected the valves.
 

·
Registered
Joined
·
327 Posts
Not quite the same, but I've been trying to dial in my 900SS. I found your description interesting. You said it's intermittent. Is it the same, that it "backfires" through the carbs while cruising at low rpm? And it does not do that if you are accelerating, correct? What do the plugs look like? Does it start up fine from cold? Any idling issues?
 

·
Premium Member
Joined
·
4,142 Posts
The valves should be checked of course (full tune w/ belts etc) but it is un likely the issue. You simply may have incorrect fueling at the rpm and throttle position. Keep in mind that bike was NEVER designed to ride at 3000rpm that may be called HD redline but more like idle on a Duc...lol. 3500 is usually tolerable but it is best to start closer to 4000 as good cruising rpms. That is Normal small Ducati engine running and is not much different on brand new efi models of similar size where low power at that rpm and very little throttle opening makes things tough.

The misfire still may be lean or rich so play with the air box lid to see if one direction is better and get a direction. this could be worn pilot jets in the carbs or too big/small a pilot jet, fuel screw setting or even synchronization. New plug wires if possible with new plugs may help as well, getting closer to that full tune. A gas tester would tell you where you are as would a dyno run with air fuel if checked in the problem area.

you might just want a reality check first though if you know another ducati owner who has a similar size bike see if theirs runs better or similar at the same rpms/throttle position before spending too much time/money on it. If the speed dictate you running at a low throttle setting and so low a rpm then look into lowering the gearing so you bring the rpms up say closer to 3500rpms at the same speed. 2-3 teeth bigger on the rear will usually get you there but verify it has not already been done.
 

·
Registered
Joined
·
36 Posts
Discussion Starter #13
Thanks for the awesome reply ducvet! I really appreciate you sharing your expertise. I definitely want to keep the expenses down. Hi JB, after I put the correct airbox lid the popping back has pretty much stopped except for one little hiccup while I was testing it. Now I'm just looking toward some fine tuning. The popping back is definitely a pain when negotiating traffic, but with me it appears to have been due to running lean. ducvet was correct.
 

·
Registered
Joined
·
36 Posts
Discussion Starter #14
Yes it was no problem while accelerating, when I put the correct airbox lid on there was a little loss in power. The plugs always look ok but the forward one is always wet with gas when I take it out. Not sure about the top one.
 

·
Registered
Joined
·
6,727 Posts
Number one cause of not running well between 3000-4000 rpm is worn needles and/ or emulsion tubes. Cleaning 37 year old carbs and not replacing wear parts is not going to work. You now have clean but worn out carburetors. I recommend Motion Pro carb tuning kits with titanium needles and nickel plated emulsion tubes ( for reduced wear). There have been some pretty detailed posts on all the things that need to be done, do a Search.
 

·
Registered
1993 750SS
Joined
·
82 Posts
Number one cause of not running well between 3000-4000 rpm is worn needles and/ or emulsion tubes. Cleaning 37 year old carbs and not replacing wear parts is not going to work. You now have clean but worn out carburetors. I recommend Motion Pro carb tuning kits with titanium needles and nickel plated emulsion tubes ( for reduced wear). There have been some pretty detailed posts on all the things that need to be done, do a Search.
Does this include taking into account mileage? E.g. low miles = less of a need to replace parts
 

·
Registered
Joined
·
6,727 Posts
They shouldn’t be that bad, but I have heard of it before. Read my old posts, there are other things to check, but that 3000-4000 range rattles the needles when they are down inside the emulsion tubes. If you spend a lot of time in that range they will wear prematurely.
 

·
Registered
Joined
·
6,727 Posts
Part of the issue is stock gearing that results in running the bike in that range a lot in town. 14 tooth countershaft or 42/43 tooth rear sprocket will result in not spending as much time in that range, so your carbs won’t wear as much. It’s TRUE !
 
1 - 20 of 62 Posts
Top