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Loss of about 10% horsepower.


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This is mostly a track bike, last year on my last session I started getting a stutter and surge of power at around 8000 rpms as if it had a second vtec. I have since replaced the spark plugs with new ngk iridium and the stutter went away even though the old ones with 2 seasons looked good, however I'm losing about 10% acceleration and top speed on the track. I have changed nothing else related to engine electrical or air/fuel. It has 60,000 miles and is due for a valve clearance check and I will be doing that but is there any other possible reasons it's lost power? I have a power commander and bypassed it and there was no change. It also appears to run rich as 75% of the time on startup it spews unburnt fuel vapor out of the exhaust.

 

Video clip of the difference

 

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Interesting video klrtovfr.

Are you sure its unburnt fuel vapour or just condensation?

- Possibly the beginnings of a ruptured/leaky fuel pressure regulator diaphragm, dumps excess fuel into cylinders 3 and 4 via the FPR vac hoses.

- Possibly one or more injectors not shutting off properly. Need to be professionally cleaned and flow balanced.

 

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8 hours ago, Grum said:

Interesting video klrtovfr.

Are you sure its unburnt fuel vapour or just condensation?

- Possibly the beginnings of a ruptured/leaky fuel pressure regulator diaphragm, dumps excess fuel into cylinders 3 and 4 via the FPR vac hoses.

- Possibly one or more injectors not shutting off properly. Need to be professionally cleaned and flow balanced.

 

It smokes for about 2 seconds but it's definitely not oil burn or water vapor. And occasionally when I get on it and someone is behind me it does the same. It's been doing that for probably the last 20,000 miles. I do have 98 catless headers and I gutted stock exhaust.

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10 hours ago, DannoXYZ said:

 vacuum leak

 

The dead give away of an vacuum leak on a Fuel Injection engine is
high uncontrolled idle... on a fuel injection system *any* air that
gets past the throttle bodies the map just adds the corresponding
fuel... the result is high uncontrollable idle... make sure all the
rubber hoses are connected and in good shape... make sure all the
intake boots are tight and in good flexible shape... if the rubbers
are hard and cracked its time for replacement...

gallery_3131_51_651212.jpg

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Other than being dirty around the throttle body. The hoses all seem fine and soft although 20 years old. I have the evaporative canister and pair removed and capped. Last time I even had the airbox removed was 5 years ago for the starter valve synch. 

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Check the vac hoses off the FPR. They go to cylinders 3 and 4. Check for any signs of raw fuel in them.

Failing that and seeing plugs, compression and vacuum are all good, seems like injectors might be next on the list and need attention.

Can't think of what else would send raw fuel out the exhaust!

 

Valve clearances, lack of clearance maybe?

 

Assume you have no active EFI fault codes? 

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So far non vtec valves are perfect in rear, front 2 cylinders are way off for both intake and exhaust were .011" spec is .014"+-.001" and intake were .005" spec is .008"+-.001" and , I'm in the process of getting the rear cams off and noticed the rear exhaust cam timing mark seems to be pointing slightly down at #3 tdc and not perpendicular as it should. Intake cam is good. Not sure if it's normal for it to be slightly off but it's been this way since 20,000 miles when last checked and now has 60,000. I will be getting the injectors cleaned, changing fpr out, and replacing most if not all vacuum lines. 

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Just wondering! If the exhaust or intake cam timing is out by one tooth, could this increase valve overlap causing excessive intake fuel to exit the exhaust? I'm no expert in this department!

 

How does the alignment compare to the front cylinders?

 

The rear exhaust doesn't look right compared to the service manual cam setup. Your photo is not showing the outboard/chain side for the index line!

 

Hopefully some of the members with cam alignment experience could chime in.

 

IMG_1125.PNG

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More valve-overlap would tend to weaken low-end torque and increase high-end power. Especially if intake-cam was retarded.

 

Looking back at OP, 10% decrease in top-speed is more than 10% loss in power, it's more like 30%!  

 

I'd get dyno-test to verify output along with AFR to check fueling. Then look for sources of external drag: wheel-bearings, brakes, chain, etc.

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2 minutes ago, DannoXYZ said:

More valve-overlap would tend to weaken low-end torque and increase high-end power. Especially if intake-cam was retarded.

 

Looking back at OP, 10% decrease in top-speed is more than 10% loss in power, it's more like 30%!  

 

I'd get dyno-test to verify output along with AFR to check fueling. Then look for sources of external drag: wheel-bearings, brakes, chain, etc.

Good Info.

Danno what's your thought on his cam alignment?

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I have a similar cam alignment issue on my VTEC. Prior to removing them, I  rolled the motor over through several cycles to get a bead on what the timing marks would look like on reassembly.  If the exhaust side was where it should be,  the other was slightly off and vice versa. I don't recall if to the extent of yours,  but it was not precise like on a 5th gen. On assembly, prior to reinstalling the caps, I initially laid one cam in properly and the other puposely one tooth off to see what that looked like.  It didn't seem as though it would be noticeable,  but it was very obvious.  It was more than just slop in the cam drive assembly.  On your rear exhaust photo I can't make out the timing - the rear exhaust mark is set by observing through the hole in the frame. I have a photo somewhere.  It's a PITA, seems like Honda could have come up with something better. Regardless,  although I put it back exactly as it had been,  the timing was never to my satisfaction.  I speculated that it could be one or a combination of factors - chain wear (30,000 miles), tensioner weakening or the slides the chains glide over wearing.  I suppose the engineers considered that when designed, over time the timing drifts some, however a few owners have reported 100,000 miles without even looking at the valves and no observable performance issues.  I would recommend once you're ready to remove the cams, put a small dab of paint on the cam sprockets and corresponding chain link - it will make reassembly so much easier. When finished, take some of the paint's solvent and wipe them off. When you roll the motor you'll need to do it again. And don't forget to release the tensioners before turning the crank. 

When I finished, I swore to myself that I would never do that procedure for anyone else or for money. It's the least favorite maintenance chore I've ever done on any of my bikes. 

 

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I forgot to mention, if you are new to the procedure,  you can make your own VTEC slide stop pins. You'll need one or two long M6 bolts that have a smooth portion of the bolt above the threads. You can cut them from the bolt like slicing a bread loaf. Worked great.  I don't recall how thick,  if you want when I get home today I'll measure them for you.  

You can also make the tensioner key from heavy gauge sheet metal. That's a bit more diffcult but doable if patient.

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11 hours ago, Grum said:

Just wondering! If the exhaust or intake cam timing is out by one tooth, could this increase valve overlap causing excessive intake fuel to exit the exhaust? I'm no expert in this department!

 

How does the alignment compare to the front cylinders?

 

The rear exhaust doesn't look right compared to the service manual cam setup. Your photo is not showing the outboard/chain side for the index line!

 

Hopefully some of the members with cam alignment experience could chime in.

 

IMG_1125.PNG

I wish that they used higher resolution photos of the cam sprocket marks. I have a hard copy of the service manual. Also #3 was my highest compression at 160, #1 was 150.

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The marks should be exactly parallel to the top of the head where the cam cover mates.  That's why the inspection hole, it's impossible to ascertain at an angle. IIRC with it one tooth off, I  could not even see the mark on the exhaust cam - so you should be able to determine if it's one tooth off.  Maybe that's why the hole is so small - AFAIK thete is no Honda documentation on that. 

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10 hours ago, Grum said:

Good Info.

Danno what's your thought on his cam alignment?

Photos does show oddity with rear exhaust cam gear. It shows marks for FI and FE, but where's index marks for RE? Gear flipped backwards?

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I'm at work now but I think RE is directly above the #3 timing mark almost where the timing mark should be. As far as I know I'm second owner since 6700 miles and the gears were never seperated from cam shaft. I did the first valve inspection at 20,000 (everything in spec) but it's been so many years since then I don't remember if the timing mark was off like that from the factory. 

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10% lost can be a worn chain or running grade 50 oil... you should look to changing sprockets and chain every 8k to 10K miles and run synthetic 30 grade because oil drag is real...

 

Blackstone's 35 years worth of racing and street motorcycle oil
analysis shows no significant differences in WEAR between the
grades... in other words either your 50 grade or a 30 grade will meet
and exceed your racing expectations... what is significant between 50
& 30 grades is HP and Temps... the amount of unwanted oil drag which
will the 2 to 3 lost of HP and the increase in Temp


full-45634-35309-oiltubeviscositytest.jp

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Dyno tests show 5% gain in going from 50 to 20w oil. SCCA mag, Silkolene ad (C/D-sport racers), probably optimistic:

 

Quote

0w-20 Advanced Development Engine Oil This maximum power 0w-20 is a unique low viscosity synthetic which cuts oil drag yet maintains a tough low-wear film on highly stressed components. Specially researched friction modifier chemistry depends upon Electrostatic Adhesion to attack friction at crucial points in valve and power train systems -- two sources of hidden power giving that vital edge in acceleration and full throttle output.

Example: 1100 cc Race Engine 15W-50 Racing Engine Oil: Max power 127.9 BHP @ 9750 RPM Max torque 75.8 ft-lbs @ 7300 RPM

5W-40 Racing Engine Oil: Max power 131.6 BHP @ 9750 RPM Max torque 77.7 ft-lbs @ 7400 RPM

0W-20 Advanced Development Project: Max power 134.4 BHP @ 9750 RPM Max torque 78.9 ft-lbs @ 7400 RPM Results:

A 5% horsepower gain and a 4% torque gain.

 

A 5% difference in Hp would yield 1.6% change in top-speed. However, there's no report of changjng oil-weights between comparison videos. 

 

 

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On 7/13/2021 at 10:08 PM, klrtovfr said:

I have a power commander and bypassed it and there was no change. It also appears to run rich as 75% of the time on startup it spews unburnt fuel vapor out of the exhaust.

 

1. How did you bypass PC? I've seen more problems caused by PC than helped.

 

2. Measure vacuum @ FPR nipple. Use vacuum-T and tap into line at FPR. What is vacuum @ idle with warmed-up engine?

 

3. Test for inaccurate MAP-sensor output as this will trick ECU into calculating improper fuel amount.

 

  3a. use vacuum-T and tap into MAP-sensor hose manifold. What is vacuum @ idle with warmed-up engine?

 

  3b. Measure MAP-sensor output-voltage at idle with warmed-up engjne. Back-probe ECU connector to get same signal that ECU receives

 

4. test TPS output voltage at idle and 5000-RPM steady speed in 3rd gear

 

 

These tests will help distinguish a mechanical issue (vacuum leak) from electronic problems with sensors and their calibration.

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7 hours ago, Cogswell said:

The marks should be exactly parallel to the top of the head where the cam cover mates.  That's why the inspection hole, it's impossible to ascertain at an angle. IIRC with it one tooth off, I  could not even see the mark on the exhaust cam - so you should be able to determine if it's one tooth off.  Maybe that's why the hole is so small - AFAIK thete is no Honda documentation on that. 

This is through the frame hole. One is slightly from bottom and one is toward the top. It's hard to photograph exactly in the middle. Also cam lobes arnt visually equally diagonal with exhaust appears to be more upward.

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Yep - mine was like that.  If it were a tooth off it would be out of sight below, and if the other way I suspect almost or out of sight on the top. Presuming the intake index mark is correctly aligned, being low like that would be consistent with elongation of the chain with wear.  I found the whole thing to be very frustrating.  If you want to satisfy yourself that the timing is correct, try what I did and install the ex cam 1 tooth off in both directions (no need to bolt down the retainers for this purpose) - my guess is you'll conclude that is correct as is, but is not as precise as hoped or expected. 

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It looks to like you're in time - wear has made it less precise.  See my reply, above. 

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