Roadie Engine Compression Question? SVS?

[Duke]

Stock pipes have more back pressure than aftermarket pipes and the headder pipes are smaller causing a little reduced exhaust flow, but a lot more back pressure. This has a big influence on the combustion chamber feeding the next air/fuel charge in the cylinder. Just as the air box can play a part in this process. It's all a balancing act in the fine tuning to get the most of what you have. The point being, is to get the most efficiency out of the set-up that you have.
Most aftermarket air filters, outside of a air box, are free flowing, and most aftermarket pipes are free flowing without the baffles being in place. Tuning the exhaust with different baffles helps bring out more efficiency in the combustion air charge, which helps increase horsepower and fuel mileage with the right carb jettings.
I have found that the 2 into 1 exhaust systems are easier to work with this tuning technique.
The 2 into 2 exhaust are different as the rear headder pipe is shorter and the back pressures, front and rear are a little different.
That being said, reading the spark plugs can help on figuring out the tune on each cylinder, although it can be frustrating trying to get it perfect. Sometimes it's good to use a colder, or hotter spark plug in a cylinder.
I find it a challenge, and rewarding when I get it close to coming together.

[rrps18admnrsc]

All the Roadstar carbureted engines are prone to SVS if they're stock and have been run with high octane fuel.
Yamaha developed "Ring Free" specifically for correcting SVS from the wrong fuel in the Roadstar engines.

It can be an issue with stock EFI engines as well, but less likely since the ECU will compensate for the wrong fuel - to a point.
Modded engines with higher compression need high octane fuel.
The Roadstar isn't one of them unless you're at altitude or have other issues creating pinging or knocking.

Intake leaks can also cause pinging, knocking under load and overheating.
Attempting to fix knocking under load with higher octane fuel isn't fixing the real problem, but it can make the noise go away for a while.

[Shotround]

2.5 on pms is too much. I went through the same experience you did with the plugs. Got fed up went the other way to 1.5 turns and it ran and ran but was hot. So opened it up some. Don’t remember where it’s at now as I use the afr guage. Try 2 turns and see from there.

my setup is practically same as yours. 2006, pump less and grizzly, stock exhaust, ra-066v filter. 40 pilot. Barons needle 4clip with washer and spacer. Ais removed. Crankcase vent to atmosphere.

I’ve experimented with different main from 167.5 up to 175. Less than 2.5 on pms is what I’ve found.

I even tried the 37.5 pilot. But stuck with the 40 as recommended.

according to the innovate Motorsport afr. I thought barons needle on 4th clip with washer was rich. Without washer was a bit lean. Keep in mind I have stock exhaust and kn ra066v filter.

I even got 39mpg with the clip on 3 with washer. I don’t recommend that. It ran way too hot. Guess I have to slow down from 75mph to get that 40mpg.

I know many of you know what you’re doing but I don’t recall you all having the stock exhaust. The stock exhaust must really be restricted compared to aftermarket comparing the difference in findings.

saving my pennies for a replacement sensor as it died after I got this far.

edit: not sure I can find enough pennies to go full aftermarket exhaust

[129drifter]

I said I would follow up on this message thread when more information was available.

I wound up replacing the whole carburetor with the other bone stock one I had.

In the process I did all the time honored Clinic procedures about removing the fuel inlet screen, Barons needle 4th groove and jetting, 2.5 PMS, Mikuni 40 pilot. I installed a new OEM enricher choke cable plunger unit, a new OEM coasting diaphragm under the aluminum cover I had, new OEM o ring and bowl o ring gasket. I trimmed the enricher knob a bit to ensure the plunger was seating properly. I bought a new OEM float and did not alter it along with installing a new Clinic recommended Grizzly needle and seat valve.

So far so good now that I have had the opportunity to accumulate enough miles to know if it made a difference. Seems to be running good and doing better overall.

[davej]

yes you can do that. I spray them with starting fluid or carb clean then put the torch to them until they are clean and dry.

[Tcontrol]

35 years in the maintenance and engineering field has taught me…
“Never say never!!! “
All it takes is a little contamination in the 6061 aluminum raw material or maybe an origination from a chinese metal forge… OP may have over torqued a screw or one may be loose… maybe the machine shop had a ‘bad ione’ slip through… it has been known to happen….

many things can compromise the integrity of what some consider a ‘Bullet Proof Design’…so i say

“Never say never”

[Lug Nut]

You may also check that metal enricher cover and confirm it hasnt warped due to internal spring tension…

I would say this is about 99.999999% not possible lol. It's thick 6061 aluminum and that sping wouldn't affect the structural rigidity if that over 10,000 years of spring tension

[129drifter]

I will be using all of this great information and working to resolve the issue soon.

Having a complete bone stock Road Star carb sitting in a box in the closet should help. May start all over again using it since It has never been tampered with and still has the TPS, enricher choke cable etc attached. I am kind of a parts pack rat and also think I have everything made out of rubber that goes in (or on) the carb still in OEM packaging that I have accumulated in the last dozen years of owning Road Stars.

This time of year it might be a month before I accumulate enough miles to know the outcome but I will follow up on this message thread with the details

[Tcontrol]

With the additional information presented regarding front plugs also indicating a rich mixture…. It becomes quite obviously a carb issue regarding a mixture….
special attention regarding the primary metering screw, the accelerator pump assembly, the main slide/diaphragm assembly and enricher attachment/ o-ring seals… is strongly advised…. You may also check that metal enricher cover and confirm it hasnt warped due to internal spring tension…

typically a leak at the float bowl needle shows itself by flooding the engine… it is easiest to check and adjust float level with the carb off of the bike using a clear tube and a level workbench… a little tang bend will be a big float level adjustment… i personally set the bowl level slightly on the low side with a pumpless bike and suggest you keep a minimum 1/4 tank of fuel to keep from fuel starving the carb at higher rpms.. ( float bowl sucks out gas faster than you can refill it using gravity at low tank levels… a minor inconvenience )
the carb gurus will advise recommended jetting with stock pipes since the pipes are still reducing your airflow through the motor… different pipes would require different jetting as airflow restrictions through the motor are reduced…

[Shores]

Why buy new plugs each time? Can't you just clean them off and hit them with a propane torch to burn everything off? Seems like I've heard about doing that.

[Lug Nut]

Maybe you're enricher cable knob is not seating fully in the closed position and therefore altering your mixture when running.

[129drifter]

The idea of too rich of a mixture is probably a good one. All four spark plugs are black each time when removed at about 1000 miles from new. I am on set number 5 or so in the last several thousand miles. The back two plugs are really black and contaminated compared to the front.. Last night I remembered that on a recent five day Smoky Mountain ride round trip from a buds house in Birmingham AL -- one of the guys following me the whole time voluntarily mentioned my bike had an exhaust odor that would indicate that.

When I first got this bike I did the time honored Clinic mod of routing the rocker cover vent tube up the frame backbone and attaching it to an automotive PVC type filter that is zip strip attached to the ignition key unit.

The plastic coasting enricher cover on the carb was replaced over a year ago with one of the metal items being sold by a few people on the various Road Star sites.

When the stock fuel pump setup was eliminated, my bud Gordon and I installed a new OEM intake manifold as described in an earlier post because my bike would not stay running without a clothespin holding the enricher / choke cable open on the way over to his house. That was well over a year ago and several thousands of miles are on the bike since then. As stated above the nipple was soldered closed and I have a rubber vacuum hose cap on top of that for good measure. I sprayed starting fluid around the edges of the intake a couple of times since then (including recently) with the engine completely warmed up and running at idle and there was no difference in RPM level

These responses are very good and I appreciate it.

This site rocks and shows how we can all learn from each other!

[davej]

Yes that is correct. see my comment above. I wrote it before I seen this post.

[davej]

What I have found in the past for this exact issue was an air leak in the front intake runner and improper carb settings. The jetting appears correct if in fact he is using a Barons needle but wrong if using a Dynojet or Speedstar needle. Unless you purchased the Barons kit yourself don't just assume you have a barons needle. Measurements on the needle will be the only way to Identify the needle. The idea of installing a float from an untouched stock carb as he asked might be a good idea as a mis-adjusted float can cause a rich condition with proper jetting.

[Brad_G]

I too wondered about an air leak skewing things. Always like to hear from the carb gurus as I learn new things from them.

[Shores]

Stupid question because I'm not a carb guru, but if the bike was jetted rich to begin with and you had a very slight air leak on the front cylinder, would that produce what he is finding?

[Tcontrol]

Missed that post… those compression readings are pretty normal … and well within reasonable tolerance…
svs treatment seems a bit ill advised just due to those readings… of course heating everything up might change things but i sincerely doubt his issue has anything to do with sticky valves…

Spark plug carbonization is most likely due to incorrect mixture or excess oil burning since compression is generally equal between cylinders…

what i find most curious is that the plugs are getting fouled pretty quickly on the rear cylinder only… a rich mixture in a common manifold should also show fouling on the front plugs as well with that low of an elapsed mileage…. Has the rocker cover vent tube become blocked and pressurized the rear cylinder top end?… are all the hoses connected correctly…?

regardless of swapping out coils… have the resistors been checked for corrosion?.. have the spark plug caps/ high voltage lead connections been refreshed… ?

maybe a carb guru can explain why the rear plugs are so much more prone to fouling than the front plugs with the current jetting… i am not convinced of that…. There is something more to this than just jetting…

[davej]

he already did a compression test

[Brad_G]

That's a good tip for how to do the test without the decompression solenoid coming into play. I'll have to remember that (although I hope I never need to do a compression test on my RS).

[Tcontrol]

You appear fixated on svs or carb at this point…

i would at least perform the easiest compression check test before i treat for svs…

use a jumper cable from positive battery to the starter with a compression gauge installed in the cylinder… you do not have to worry about the decompression solenoid interferance at all… heck.. you do not even need to turn the key on… just turn the starter over with the jumper cable to battery connection to pump up the cylinder….. it aint rocket science…

you would be surprised what a simple test procedure can tell you before you delve into more complicated tests…