I just got my 1990 1000f back from the shop after having it rejetted. I put on a full vance&hines system 4 into 1. Now the bike is backfiring when I let off the throttle. It also has a lot less power in the lower rpm's. For the first 5000 its real erratic. The tech at the shop tells me that the power loss in the lower rpm range is normal and its running exactly like it should. I told him I thought he was crazy and I was going to take it to someone who has rode a 1000f before. Valves seem a bit noisy too. If anyone has any sugestions for me, or if I was out of line and owe him an apology I'm all ears. Thanks

 

hi all

tell ur tech guy he s nuts (not normal) i have V&H ss2r system no backfire no poping just steady power all thru top and bottom rpms and sounds like a dream
(wet 1 at that) i have heard no other system that **** close

must b jetting prob u will learn more shortly from the tech guys on here there great

good luck

find another shop i will try and add sound bites 2morrow if my cam will pic it up half way decent i will record sry cant try 2night V&H downfall neigbors get mad

 

Sorry dude, but he is right. When you put a 4-1 on you loose a lot of power down low, but gain it up high. That is why a lot of big road bikes from new have 4-2-1 or 4-2 and race bikes have a 4-1.

Some popping is normal with a re-jetted & piped bike as they tend to run a little lean for more power, but if its excessive you may have to get him to raise the needle and/or put in bigger pilot jets. But you'd need to put it on a dyno and see where the a/f ratio is at.

If I could I would give up my 4-2-1 system and go back to stock 4-2 (or aftermarket 4-2).

 

Hello,
I to had a problem with it popping under decell when i put the vance hines exhaust on my 94 The system i put im mine is the cheaper one than the ss2rmines the 4-2-1 i also installed a dyno jet kit ran the d124 jet with the e-clip on the needle on the second groove down like it said in the instruction.. bike ran good seemed to have more top end power didnt seem to lose any bottom end like what your saying.. but was runnig really rich when i layed on it hard.. im at about 4500ft elevation so i put the stock 122 jets in put the eclip up a notch that helped but what i think help the popping most was removing the pair valves and all emissions.. i also had the carbs synced
i was just thinking you say the valves are making noise if you have a exhaust leak at the head pipes that will also cause popping though the exhuast from sucking cold air.. maybe the valve noise you hear might be exhaust leaks??
my bike still pops everso slightly if i decell below 3500 rpm but i think it pretty normal is your bike a california model?? id get a stethoscope and pen point the noisemaybe the mechanic didnt change the copper seals on the exhaust ormessed them up installing them -hope this helps let me know

 

I'm with Trips on this one.

Picked up my 87 with a set on F1r slip ons. Loud but decent spread on the power band. Sold the slip ons, stored the oem header.

Jetted with Stage 1 and mounted a V&H Supersport 4 to 1 and a full carb Sync, Valve adjus and tune. Great look, lightweight and throaty low end in traffic.
The lower power band was displaced to the upper end.
After aflat spot/stutter around 5 to 5 1/2 rpm it pulled hard and strong up to redline. It made for some rather faster riding just for the Feel of it.
I think that thestraight through non-restricted flow (even with the Q**tec Baffle)is the culprit for yourback firing, if the rest of the system has not been adjusted properly.

Wanting a return to a broader and Usefull powerband for me, I decided to graft a ZX10R can to the V&H header. Sold the V&H can.
So far, it's been successful. The back pressure has spread the band better for me, eliminated the 5K flat spot, looks feels and soundsfine.
I'm hoping not to have to mess with the jetting again. I'm guessing that the fuelmilage has suffered some with thestage 1 set up.

I like the 4 to 1 set up and look but may have stayed witha 4 to 2 set up ifa set of slip ons were easily available/affordable.





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Thanks for the info all.
The Vance&Hines system is a 4 into 2 into 1. But after looking at it closer it looks like I have 2 bad exaust leaks. One at the header and one more at the connection under the bike where the where the second pipe connects. I'm hoping that when I seal both leaks it will run better and have less noise up front.
I might have believed the mechanic if the problem was only where the power started. But with it acting so jumpy and unpredictable in the lower range I knew he was crazy.
Thanks again for the info I'll let you know how it runs with the leaks fixed.

 

I am with Trips also.
Most 4-1 systems are tunes for max performance, V&H especially. To get the most power at max RPM you need to have as little backpressure as possible. You need back pressure for low RPM grunt. That is also in agreement with Bay Area Rider.

The 4-1 (or tuned) systems work by the principle that when the exhaust valve opens, a high-pressure blast of hot gas is expelled down the head pipe. It only stands to reason that following the high pressure is a low-pressure volume. When the system is tuned correctly, the low pressure is just beyond the collector pipe and helps draw the next high pressure volume into the collector pipe. At low RPM de-acceleration, due to the lack of back pressure and the sucking force of the tuned pipe, some small amount of raw un-burnt fuel is drawn into the head pipe and is ignited by hot gasses in the collector pipe causing the backfire or popping.

Tuned 4-1 pipes work best at full throttle.

 

becareful trying to fix where all the pipes join up, that's where the metal is the thinnest and a welder might just blow right through any metal that is left. (what happened to my pipes)

 

the header pipe to the back pipe with the springs connecting them will leak slight since it just slips in id worry about your head pipes.. if there leaking i bet that the main cause of or problem because under decell itll suck colder air which will cause it to pop.. theres definatly a problem like i said my pops slightly below 3500 not to bad..but this system isnt a 4 into 1 shouldnt be poping like your saying, so sorry guys i dissagree not normal

 

Cruzn, after reading your post that mentioned the head pipe leak, I went back and read teubert1162’s original post. I missed the part about the noisy valves. I agree with you also. When the low pressure volume is at the head/head pipe interface, it draws cold outside air into the pipe where it expands many times bigger causing a blockage. A big drop in power is experienced. The clicking noise heard that sounds like noisy valves are the rapid expansion of the cold air in the pipe when the hot gasses slam into it and expand it. The bike would be a bit jumpy at lower RPMs and clear at higher. It would also pop.
What was said above also is true. 4-1 (tuned) pipes are best at the track but not for all riding conditions.