Carb Rebuild, New Fuel Lines and Selector Now Bogging Down when throttle pressed

[Stal8080]

Hello All,

After two years, I pulled my 95 XP 720 out of storage. Had original fuel lines---now all replaced, along with new fuel selector, few new oil lines, new fuel & oil filters and carbs were rebuilt with new needles as well.

After first water test, noticed few issues:

1. Fuel gauge now does not work
2. RPM gauge does not work
3. Biggest Concern---Ski seems to bog down before reeving and getting up to top speed. If I punched it from a stopped position ski seems to bog like I just sucked up a ton of seaweed. It will get going but takes a bit.....thoughts?

 

[Bills86e]

Forget to do wire re-connect before closeing the hood? What do plugs look like? Whats the compression? Go back over the supply line connections and re-tighten. Both carbs pop-off to spec and within 1 PSI of each other? separator cup snug?

 

[Mickirig1]

Replaced accelerator pump diaphragm if it has? Check fuel system for air leaks.

 

[Stal8080]

Replaced accelerator pump diaphragm if it has? Check fuel system for air leaks.

Thanks for replies, I don't believe 95 XP 720 has accelerator pump but I could be wrong....anyone know if ski should have it?

 

[Matt Braley]

No it does not have it but it does have a pop off of 50psi or more so there is a lot of opportunity for leaks. Did you change the little springs under the inlet needle rocker? If so that could be the issue.

 

[Sportster-2001-951C-Stock]

I vote for a fuel line air leak somewhere, fuel pump is sucking air not fuel or the carbs are plugged internally By "bog" I think you mean the engine is lean-stalling.

 

[tkarvelis]

Did you use an oem rebuild kit?

 

[Sportster-2001-951C-Stock]

Did you use an oem rebuild kit?

This is a very good point. I've found IMO, only SOME of the parts in various aftermarket Mikuni kits are reasonably made. What I mean is, if you were to use all of the parts provided, it's likely your carb won't work exactly as it did when new.

For instance, the oval mylar check valve that mounts with a single screw onto the kidney-shaped metering plate is often of the incorrect thickness and elasticity thus causing a slight delay to the main veturi sensitivity. This delay can cause a lean hesitation just as the main venturi should begin flowing.

From my perspective (FWIW, you decide 4 urself):

Further, IMO these aluminum carburetors have very small precision-drilled transition ports (aka: pilot ports) that corrode internally and thus become restricted over time, as a result. These can present a real challenge to restore complete diameter and must be checked very closely. The symptom I've experienced has been a part throttle lean hesitation that occurs somewhere between off idle to before or just as the main venturi begins to flow. Most of the entire fuel tank consumed by the engine is delivered through these tiny passages unless you tend to ride primarily at the upper range of the throttle travel.

 

[Stal8080]

Did you use an oem rebuild kit?

Rebuild kit was from JSP Manufacturing and the needles were from SBT. I know before we put them back on pop test was within spec and within 1 psi of each other.

 

[mikidymac]

Rebuild kit was from JSP Manufacturing and the needles were from SBT. I know before we put them back on pop test was within spec and within 1 psi of each other.

99.9% chance that is your problem.

We all say only OEM carb parts for a reason.

I can't tell you how many times a season we hear this same story and it is almost always the aftermarket carb kits.

The $120 is not that bad to do two carbs with OEM kits compared to buying the cheap ones for $80 then having to buy the OEM ones anyways.

 

[Mickirig1]

Read the sticky above forum about carbs. It gives great advice about cleaning and tuning. Breaks down what parts do what, in the ranges. Helps you narrow down where the problem is, in the throttle curve. When it bogs pull chock. tells you it is lean if it runs better.

 

[pwgsx]

I would say its the sbt kits or dirty carbs still. I cant tell you how many times someone tell me they rebuilt the carbs and when I get them, they are still dirty. They need to be spotless on the inside.

 

[Coastiejoe]

If you didn't use OEM kits, needles and seats you are chasing ghosts. The carbs are one of the items that really must be OEM Kits. Much like starters and solenoids.

 

[Stal8080]

I vote for a fuel line air leak somewhere, fuel pump is sucking air not fuel or the carbs are plugged internally By "bog" I think you mean the engine is lean-stalling.

Finally got back to looking at ski.....definitely air in fuel lines--lots when starting/running ski. Don't know if that is what is causing issue with bogging---but could be???

Re-seated electrical connections and fuel and RPM's don't work still. I'm guessing because fuel sat 2 years in tank, it ruined fuel sending or level is stuck????

 

[pwgsx]

Did you use a OEM fuel valve? Im guessing you used a sbt or knockoff/used one??

 

[Mickirig1]

My often answer is check the fuel system for leaks. The pop tester can be used for testing. The procedure is in repair manual. CoastieJoe can tell you. I chased the same problem for a month till I found the leak. Check for a cracked nipple on some plastic parts. Look for a crack on fuel filter. Look at under front hatch filter / water separator. gasket goes bad or missing a lot. The vents / air in valves may be bad. They need replaced periodically, due to age. Procedure is in repair manual. Part of pressure test of system.