Hello pals,

This is the issue:

- I repaired the top end (blown valves, worn seats, a full head rebuild) about 6 months ago;

- I have a HD Sportster muffler, with some minor leaks at the connection to the headpipe, and it has been running fine;

- All the engine gaskets are fine, no leaks, and tight;

- Last week, as I was commuting to work, the bike seemed to lack power, and felt as if it did not want to accelerate, and on my way back home, it could barely get to 30 mph, with full throttle;

- My mechanic found the valves to be out of adjustment, and the admission valves did not fully close, allowing extra fuel into the chamber, which explained the black smoke and lack of power;

- He adjusted the valves, changed oil, put a new spark plug in, new oil filter, and the bike started up great;

- However, he thinks my HD muffler may be causing an excessive back pressure into the engine, and keeping the valves too hot for too long, and he claims that it will affect/destroy my valves in the long run. He suggested me to find a new muffler, with less restriction. I do not want to do that;

- He wants to kow what the operating temperature inside the engine should be, in order to determine if we are running too hot inside or not (I don't know if anyone knows, keep in mind my bike is a 400cc, chain-drive);

- This morning, as I was commuting to work, the bike felt as if it was hesitant to accelerate over 55 mph; weird, as just before all this happened 60-65 mph were not a problem;

What's wrong with my engine? Is he trying to BS me?

I trust him, but this is just weird.

Thanks for your help.

Ride safe,

RW

Hey RW!

Hmmm.... too much back pressure?  Sounds like BS to me... remember how restrictive the stock muffler was?

Random power cutting out or just a degradation in power sounds like a bad electrical connection or bad fuel delivery.

for the electrical conxns... well, you gotta go through the system... but I'd also check the ignition coil.

fule delivery... check the petc0ck, vacuum line, and fuel filter.

I'm sure others will chime in.

Good luck!

the service manual lists the following possible causes in the troubleshooting section.

1-loss of valve clearence
2-weakened valve springs
3-valave timing out of adjustment
4-worn piston ring or culinder
5-poor seating of valves
6-fouled plug
7-worn rocker arms or shafts
8-plug gap incorrect
9-clogged jets in carburetor
10-float chamber fuel level out of adjustment
11-clogged air cleaner element
12-too much engine oil

At least you have some idea of where to look. I always look at the easiest and most available remedies first. good luck.

How many miles after the head rebuild had it been?  General rule of thumb is if you do a full valve job then the first valve clearance checks need to match that of a new engine.  I haven't looked at the manual but usually for suzukis of that design it was about 500-1,000 miles.  This is to make sure the the clearance is adjusted after the valves seat in.  I had a GSX-R that I failed to check compression before buying and it was leaky intake valves.  needed a full valve job the we are willing to bet it was early in it's life when it was neglected as the valves were right on when I bought it.


Assuming that it ran well after right after you put the new muffler on then I would have them check the valve clearance again now that it has been run.  Normally you would wait that 500 miles or what ever is recomended on a new bike but it sounds like you have issues.  The other thing to consider is a compression check.  If the valves are held open again it will show in low compression.  If they get that they can add a teaspoon of oil in the sparkplug hole to seal op the rings and that will tell if it is valves or rings if you do in deep have low compression. (I would still check valve clearance per the porcedure with feeler gauges as it is so easy to access on these engines)

If the compression is good and valve clearance is ok then confirm the jetting is right.  If you put a less restrictive exaust on it then you most likely need to re-jet if you haven't.  If it is lean then that indeed can cause both power losses and engine damage if run for a long time in that condition.

Good luck!

Red_Wine wrote on 12/31/69 at 16:00:03:



RW,  Based on what you said if you have more than about 500 miles in those 4 months I would pop the valve cover inspection ports and check the valve clearance per the manual.  

That would be precautionary and wise.  Your problem however sounds like it may be more jetting based...more on that in a minute.

Compression is built of course when the valves are closed and the piston comes up.  If you have low compression there is a leak somewhere.  It either goes out past a leaky vavle or the piston rings.  The valves generally leak when they are held open by improper clearance with the cam (valve adjustment), built up carbon deposits, or burned seal areas.  The last is usally a long term result of valves being held open and running that way or high heat build up (lean running etc).  The rings will leak is worn out, broken, or scored cylinder.  

When you check compression and it is low you don't know if it is going past the valves or the rings.  What you do then is pull the compression gage out (that you screwed into the spark plug hole) and pour in a teaspoon of oil.  Turn the engine over a couple of times to distribute it and then check compression again. This seals the rings from the top like you said.  If the compression is now good you know it was the rings.  If there is no change then there is a valve that is not sealing.

(the last not mentioned item is if you have a blown head gasket but that usually has other indicators such as hissing noise, viusal leak/burns)

Now yours is not building power on the top end.  If you didn't rejet after that muffler I would look seriously at your jetting.  You can build false compression at high rpm.  that is what my GSXR did. It idled lousy but ran great at high rpm.

When running lean you build heat and start to loose power especially if you start to detonate.  I had a two stroke in this condtion that could bearly limp it's self home.  

Now the only thing you didn't answer was did it run correctly after the new pipe or was all the work done at the same time?  if it was all done the same time I would check the valve clearance and then go after the jetting.


Good luck

Red_Wine wrote on 12/31/69 at 16:00:04:


I wouldn't worry about needing new valves until you check the clearance under the tappet (and then compression).  That is where the threaded adjuster is inside the little inspection windows.  You will want a manual to follow but basically if you follow the procedure you end up setting the cams at particular points and then check the clearance between the rocker tappet and the end of the valve.  It is common to recut the valve seats and dress the valves.  Then like noted before you need to check/adjust the valves usually somewhere around 500-1000 miles later.  I definately would start there.

Savage_Greg wrote on 12/31/69 at 16:00:04:



Ya know...I have heard Hardleys discribed as having a Potato..Potato..Potato sound.

Hello fellow Savagers,

Here is the latest update:

- My mechanic opened the top end, and found the intake and exhaust valves to be burned up. Also, the retainers and seals were shot. The top of the piston had a thick layer of charcoal dust-like on it. We could scrape if with a finger nail. He claimed it was the result of an excess of fuel mixture coming into the chamber.

- We decided to replace the valves (something we did not do 6 months ago, when we repaired the camshaft, timing chain, valve seats and seals, piston rings, etc.).

- The bike was delivered yesterday, and it sounds very different. The engine feels "tight", without any metallic rattling or anything. Just a lovely "tump, thump" when idling.

- I am supposed not to exceed 80 kph for the next 500 kms., before a re-tightening and oil change is made. Then, it will be free.

- I will have to keep an eye on a exhaust leak developed at the junction of the head pipe and the Sporty muffler I have. I may need to weld them solid to keep it airtight.

That' all for now. I'm back riding, which is great for a mid-fall season. It's been very variable lately in this neck of the world, but I'm glad I will only see snow on the mountains, not on the city.

Comments welcome.

Take care,

RW