My cbr600 had an issue where no matter what gear it was in, if I just ripped on the throttle from no throttle, the bike would stay around 2000 and just bog. Holding it at WOT it would just bog and not increase in RPMs. This happened in neutral, in gear, in gear with the clutch pulled in, while moving in gear... As you can imagine this is not good and even unsafe if I was pulling out into traffic. So I had some poorly spliced wires in the harness for the fuel injectors and the TPS sensor. I replaced the section of harness that was bad with OEM harness. The Throttle position sensor on these bikes is made into the TB requiring the whole TB to be changed if i determinaed the TPS being bad. I did some testing on it and determined the TPS was bad. So i bought a "tested tps throttle body" from ebay and installed it back onto the bike. While the bike was apart, I replaced the fuel filter in the tank and the spark plugs.

Now after putting it all back together, the bike still bogs down when on the throtltle. Itll get me from point A to B but it doesnt move out of its own way at times. I have attached a link (I hope it works) showing what its doing to hopefully gain some knowledge on it. On the high end of the throttle, 10k and up, the throttle response is fine but idle to 6 or 7k, its like the TPS is bad. I just got done putting it all back together so I am done messing with it for today but i plan on looking at it some more tomorrow. I havent tested anything yet since putting it back together.

https://www.youtube.com/shorts/ce0LpWGe00w

Has anyone experienced this before or is anyone familiar with this happening? Thanks

 

That doesn't sound like it's running on all four - did you check to see if you have a cold downpipe?

 

1. Post your measurements of TPS sensor output voltage at idle, 0% and 100% at sensor itself. Then repeat same measurements at ECU connector. 6 numbers

2. Repeat same test for MAP sensor at idle, 50% and 100% throttle. At sensor itself, then at ECU connector. 6 numbers

3. use vacuum-T and tap into MAP sensor vacuum line to measure actual vacuum levels at idle, 0% and 100% throttle. InHg 1,2,3=???, 3 numbers

 

So this morning, I let the bike idle with a few throttle inputs to keep it idling , and measuered the temp of each header. Cylinders 1 and 4 were about 180f and cylinder 2 and 3 were 280f to 300f. The temp of the bike wasnt high enough to make the fan kick on so that was just the bike sitting still. Obviously this means 1 and 4 arent firing as much if at all compared to 2 and 3. When I pulled the plugs last week, all 4 looked about the same. It did backfire once while giving it throttle which it hasnt done before. I also smelled fuel this morning when i started it up so maybe 1 and 4 arent firing?

I am going to work on testing the tps now so ill have those numbers here in a little. I did notice a slight improvement to throttle response since the video was posted but maybe its just me over thinking it.

Thank you

 

TPS Sensor voltage at sensor:
idle: 0.460
50% throttle: 2.260~
100% throttle: 4.4v

TPS voltage at ecu
idle: 4.7v
50% throttle: 2.30v~
100% throttle: 4.4v

I began to measure MAP sensor voltage and was having trouble determining which wire to test. The wire i got a voltage reading from was the Yellow/red wire, which looking at the wiring diagram, I found it was shared with the TPS. The only reading I got from it was 4.3v. No matter the position of the throttle with the bike running, It was always 4.3v. I did notice with the TPS sensor readings, if i turned the kill switch to the off position, the readings dropped very low (im assuiming this was normal.) I am going now to pick up a vacuum tool to test the vacuum readings on the map sensor so bare with me.

Thank you guys in advance and I'll post the vacuum measurements shortly.

 

So i got the vcauum gauge hooked up and started the bike. Theres a section of green on the guage and it indicated that is where a " normal car motor" should stay at idle. My bike stays at 4-5 in/vac. I can blip the throttle and get it up to 15 in/vac but never up to the green range which is 17-22. The guage states if it is in the lower red section, that there is a leak at intake manifold or late valve timing. I am unsure if the valves were ever adjusted on the bike. Since the bike sat for over 6 years, i am leaning towards there being a hole in a vacuum hose bc there were signs of rats when i got the bike. The only way i know of finding a vacuum leak is to let the bike idle and spray starting fluid at spots where there could be a leak and if the RPMs go up, then that is where the air leak is. Looking at it now, i probably shouldve replaced a lot of the rubber hoses (coolant and vacuum) hoses on the bike while i had the TB off but i have too much time invested into this bike to quit now so i guess im looking for an air leak.

 

UPDATE:

I bought a smoke machine from amazon and tested the system today after work. I found smoke coming from between the bottom of the airbox and the throttle body. Upon inspection of a parts diagram, I found there was supposed to be a seal there as well as a seal between the top and bottom sections of the air box. I have neither of those seals and never have installed them on the bike. I ordered those and hope those will fix my vacuum issue. I shouldve known plastic and metal arent good mating surfaces to keep air in.

I also noticed a typo in my measurements of the TPS voltages. The voltage at idle was supposed to say the same at the sensor as at the ECU. The correct measurement was 0.46v.

I will update this thread once the seals for the air box and throttle body come in for anyone else having a similar issue to reference. Thank you all for the help.

 

These are good tests! Looks like TPS is fine.

Vacuum might be OK for cold engine. Leaks before throttle-butterflies won't make a difference in operation of bike. Vacuum only exists after throttle-plates due to their restriction. Might want to

1. do compression test, low here can also contribute to low vacuum

2. if low, measure valve-clearances and adjust as needed.

3. re-measure vacuum at idle and steady 3000rpms

4. measure MAP-sensor output-voltage on lg/yel wire at ECU connector. Can back-probe connector with thin probe, or sewing needle. Other 2 shared wires with TPS are reference-power and ground, so ignore those


I think we're down to ignition as primary culprit.

5. Pull out coils and take close-up photo of their part#. Compare to photos of genuine factory OEM parts to determine if they are genuine or fakes. There's so many crappy 3rd-party aftermarket parts that are bad right out of box and needs to be tested and verified good before using. Even then, they won't work as well as factory OEM parts.

Only buy factory OEM parts from authorised Honda dealer!! Especially electronics.

6. do spark test. Pull 1 coil and insert spare plug. Ground case of plug to bare metal near head. Run engine, do you see bright blue spark? Rev engine into troublesome range. Does spark remain steady with bright blur spark? Or does it skip sparking sometimes and is sometimes dim orange color?


Here's guy that fought this issue for YEARS!!! Did everything possible. Had given up and about to sell his bike. Turned out he didn't use factory OEM parts...
https://www.st-owners.com/forums/thr....177612/page-9

 

UPDATE:

Did a compresion test on the bike today after work. Per the service manual, spec is 178psi. Cylinder 1, 2, 3, and 4 all had low compression. Respectively, the cylinders had 82psi, 85psi, 85psi, and 65psi. After 10 minutes of sitting with gauge hooked up, each cylinder leaked down to 70psi, 70psi, 63psi, and 60psi respectively. It is worthy of noting cylinders 1 and 4 spark plugs came out clean with no oil on threads. Cylinders 2 and 3 spark plugs came out slightly fouled with a small amount of oil on threads and tip. Cylinders 2 and 3 were the ones with higher header temps.

I went back to look at my purchases when I was putting the bike together the first time and found my purchase for the coils. Out of all parts ordered, the coils were one of 2 things that were NOT OEM honda parts. The coils appeared to be fine but obviously could be bad. I did not bother testing coils after getting low compression readings. I have attached the link to the coils I bought. I have also attached a few pictures of the coils I had in the bike. The coils I have in the bike do not have any part numbers on them. I would be fine with testing each coil however I dont think it is worth investing into the bike if I possibly need valves adjusted or piston rings replaced.

https://www.ebay.com/itm/361999320514



Thank you

 

You're welcome! Good job on compression tests!

Status of coils really unknown due to lack of compression. Let's ignore them for now as low-compression is contributing more to this problem than anything else.

Most likely just tight valves. Lack of vacuum would certainly throw off MAP-sensor and cause ECU to inject improper amounts of petrol.


1. Wouldn't hurt to do piston soak. Squirt 5-8sec of PB-blaster down each spark hole. Follow with 2-3cc 50/50 mix of acetone/ATF. Slowly spin engine over by hand 360-degrees and let sit 12-hrs

2. While pistons are soaking, measure valve clearances and see how far off-spec they are.