Can spark plugs cause power loss at certain RPMs?

[safwan.khan]

Hi folks.

I have a 1988 Suzuki GS450 which is running great after top-end rebuild. I have recently been playing around with the spark plugs since I tried but could not find NGK B8ES which are said to be the best plugs for these bikes. I have tried Denso W20EX-U and NGK BP5EY and NGK BPR6EGP (platinum tip ones). The throttle seems to be a little (by little I mean VERY little) bit laggy to respond when I am on BP5EY and it is relatively better on W20EX-U however I have a feeling that it can be much better as I have ridden other similar bikes which have awesome throttle responses. I got a pair of BPR6EGPs today from a fellow mechanic which were in good condition and I thought to try them out.

I noted that the throttle response was much smoother than the other two and the bike seemed to have gained a little bit of pick. But, when I took her on a long highway and pulled that throttle to the end, I noticed that there was sudden power loss at around 7000 RPM and my bike couldn't cross 140 Km/h. On Denso W20EX-Us, I had touched 160 with no problems just yesterday. What do the experts here have to say about it?

[TopTechRacing]

The NGK number you are using are way to hot for the application. The stock plug also is a non projected tip plug. Running these at high speed could cause detonation and hurt the engine.

http://www.ngksparkplugs.com/tech_support/spark_plugs/p2.asp?mode=nml

[Guest]

You can buy the NGK B8ES plugs from eBay retailers that ship to Pakistan.

[Nessism]

All the major plug manufacturers have cross reference guides. Look up the cross reference for B8ES and then go find some. http://www.sparkplug-crossreference....rt/NGK_PN/B8ES

[eil]

I'll also add that poor throttle response is usually (but not always) a result of carburetor issues.

[Badooka]

Valves get adjusted after the rebuild????

[safwan.khan]

I've monitored my plugs regularly and so far there is no sign of detonation on the ceramic insulator. Perhaps may be because I've not taken my bike on a very long tour yet and mostly it travels less than 20-30 km a day, majority of the distance at slow speed as it's a crowded town area. I've looked at the compatibility list and found that Denso W24ES-U are compatible with NGK B8ES but the irony is that for some awkward reason, only hot plugs are available in the local market. Perhaps because of the crowded streets and too much plug fouling complains on colder plugs due to that reason? God knows.

The NGK number you are using are way to hot for the application. The stock plug also is a non projected tip plug. Running these at high speed could cause detonation and hurt the engine.

http://www.ngksparkplugs.com/tech_su...2.asp?mode=nml

[safwan.khan]

My carbs are crystal clear as I've cleaned them recently.

I'll also add that poor throttle response is usually (but not always) a result of carburetor issues.

[safwan.khan]

Yup. Valve adjustment is a part of top-end rebuild.

Valves get adjusted after the rebuild????

[tkent02]

I took her on a long highway and pulled that throttle to the end, I noticed that there was sudden power loss at around 7000 RPM and my bike couldn't cross 140 Km/h.

This sounds like the main jet is too small. Not sure why it would react differently with different plugs.

[safwan.khan]

I just pulled the plugs (NGK BPR6EGP) out for analysis.

Here is plug 1: https://www.dropbox.com/s/i3nxn4c4i8...920%5B1%5D.jpg

Here is plug 2: https://www.dropbox.com/s/ncvi516gre...822%5B1%5D.jpg

Apparently the plugs look fine (no signs of detonation / pre-ignition so far) but since it is late winter season so that could be a factor. I've put Denso W20EX-U's back in as they were allowing me to reach higher RPMs with no power loss.

I surveyed the market and apparently NGK BP5EY, BP6EY and Denso W16EX-U, W20EX-U are the most commonly available plugs in my area. I guess i'll have to import B8ES for my machine from abroad.

[tkent02]

Another thought, have you got enough fuel flow from the petcock to keep the float bowls full at wide open throttle?

[Nessism]

The running problem is almost certainly not because of the spark plugs.

[TopTechRacing]

This sounds like the main jet is too small. Not sure why it would react differently with different plugs.

Detonation.

[TopTechRacing]

The Hotter plug may work fine for local low speed running but the issue I see is you are at least 2 to 3 heat ranges too hot for high speed use and you couple that with a projected tip sitting in the combustion chamber and you have a good chance of hurting the motor at high sustained running. I see this happen a lot in race engines for cars.