CARB Problem 96 GSX - GURUS, Warriors?

[etemplet]

1996 GSX complete rebuild, Let's just say I checked everything and I've been fighting these "new carbs." They have accelerator pumps. The ski is difficult to start. When I gave it more fuel through the low speed adjusters it improved a degree but still very difficult on the low end. I moved the 67.5 jets to 70 and I am probably 2 turns out on the low speed adjusters... I can't see. Took the ski to the water and it feels like it is losing a cylinder around 3000 rpm. A gentle jab on the throttle and it picks right up. Likely a squirt of fuel from the accelerator pump alleviates the problem. Problem seems to be at 3k and I'll call it a flat spot. It feels like only one cylinder but I'm not going the "it feels like route' If let of the throttle the engine will continue to run pretty well. Top end is terrific, ski is strong.

I'm wondering about quality control on these carbs. They came with different main jets (140) and (142.5) and (67.5) low speed. Switching to the (70) low speed made it better in the shop. I lowered the pop-off which my gauge had at 43 psi. I reset pop off with the 80 gram spring and I'm reading 33. My gauge could be off. I have a couple of options but I'm not sure what will happen. I could lower pop-off again and shoot for another 5 psi. Has anyone had to install (72.5) jets ?

I tested the fuel system, replaced the fuel selector and pressurized the system. It just seems the ski is not getting fuel. Help suggestions are appreciated.

NOTE: I have another set of carbs for this ski and I'm very tempted to go through them and put them on. I just don't want to do all that work.

 

[etemplet]

I disassembled the initial carbs the owner had for the ski, before he purchased the new ones. They were clean and clear but... Of course, cheap non Mikuni parts were installed so they would never have worked. I'm gonna build these and install them on the ski.

 

[etemplet]

Well well well... so I have a question for carb aficionados... so IF the return line back to the fuel tank is restricted or blocked... what effect would that have on the fuel flow to the engine? Would the entire system pressure up and the fuel pump not have the ability to overcome the restriction thus... stop functioning? Then when I pump the throttle the engine gets fuel through the accelerator pump and accelerates thus burning more fuel and alleviating the pressure build up inside the carb. This might seem deep but something like this may well be the problem.

THIS is the reason I don't work on other people's jet skis... you have to find every issue. Restorations are easier because I replace just about everything. What I found on this system was a few problems at the fuel baffle and in the tank vents. The fuel tank vent valve isn't working because the fuel tank is pressuring up while sitting ( Last week while preparing to refuel at the gas station I thought was strange when I opened the cap and got a big puff of air when I removed the fuel cap) I decided to check carb return line and after I removed it from the baffle I found baffle nipple "crushed." I blew through the return line from the carb to the fuel tank and a blob came out. Now I'm under the assumption that this blockage was restricting fuel flow back to the fuel tank. So.... if the fuel can't return to the fuel tank... the fuel pump can't pump. THIS MAY BE the CARB PROBLEM. Boy O Boy I love these games but they can be frustrating. Whatever don't kill ya makes you stronger !!

I verified the Fuel pressure vent was plugged. I think these few issues with the fuel tank and lines may alleviate the strange carb problems.

 

[tobytd]

Don’t forget that the carbs have restrictions built into the return circuit.

 

[etemplet]

I ended up removing and replacing the fuel baffle. I just had so much trouble getting the fuel to the carb I wanted to check everything. I rebuild a second set of carbs and installed them. I had to open the low speeds a bit more than book but the ski is idling and responding like it should. I just don't get the problem with the new carbs. I just don't have the desire to keep messing with them but I'd like to find out if I could make them work. They are simply way lean on low speed and upsizing the jets and opening the low speed adjuster 2- 1/2 turns didn't do anything. Still lean as hell on low speed and would "sing" at idle when I gave it throttle. Took a long time to drop down and was still lean at idle.

 

[Stevie96xp]

I would swap to oem carbs they are probably after market carbs and the ports are probably built too small

 

[etemplet]

I would swap to oem carbs they are probably after market carbs and the ports are probably built too small

Interesting. I took the apart and adjusted the pop-off, replaced the jets and such. I'm pretty sure they were mikuni but couldn't testify to that. LOL I know the owner paid $500 for the carbs.

He did ride the ski and loved it !! said it was too fast for him. LOL

 

[Stevie96xp]

Interesting. I took the apart and adjusted the pop-off, replaced the jets and such. I'm pretty sure they were mikuni but couldn't testify to that. LOL I know the owner paid $500 for the carbs.

He did ride the ski and loved it !! said it was too fast for him. LOL

Well good glad you got it figured out. I’ve seen that aftermarket stuff be really crap and some times is just as good.

 

[etemplet]

Well good glad you got it figured out. I’ve seen that aftermarket stuff be really crap and some times is just as good.

I rebuilt his old set of carbs. Didn't use his new ones.

 

[Stevie96xp]

I rebuilt his old set of carbs. Didn't use his new ones.

Yeah it’s crazy what will work and what won’t

 

[etemplet]

Yeah it’s crazy what will work and what won’t

I could have kept playing with the new carbs (they had an accelerator pump) I changed jetting, lowered the pop off, and could not clear up the bogging. After 3 tries I decided to go with the old carbs and rebuild them. Ski worked fine right away. Very strange but not the first time I've seen carb problems like that. Thankfully the first time wasn't on a ski I worked on. LOL The mechanic in me would like to get those new carbs working but I spend enough time on weird searches. Ha ha. Have a good one !!

 

[Venturian1]

Don’t forget that the carbs have restrictions built into the return circuit.

My 98 GS and GTS with single carbs and equipped with accelerator pump, have a restrictor jet inside of the fuel hose that feeds the accelerator pump. The book may have referred to it as a recharge jet, as it slows the rate the accelerator pump reservoir refills.